Since the original article on Oiling The Action was published I've had a few emails from repairers and seen references on various web sites which claim that this method of oiling the action is ineffective.
This has always surprised me, given that my standard 'lecture to a lazy client' involves placing a drop of oil at each end of a rattly key's barrel and then working the key as the oil wicks in. It's an effective demonstration, as both the client and I can hear the rattles fade away as the oil does its work.
But it's been suggested that the oil is only getting part-way into the barrel (if at all) - so I put my 'myth-buster' hat on and set up a small experiment.
I approached the project with an open mind - I was pretty sure that the visible results would match my hands-on experience, but I was more than prepared to accept being proved wrong. As it turns out, I found out more than I bargained for...

I dug out an old 'beater' sax, cut the key arms off the G# key and replaced the barrel with a stiff acrylic tube. I then made and fitted a rod screw, and just to make it a tough test I made sure the rod screw was a very snug fit. I glued the key arms in place and fitted a spring - with no spring cradle on the key I simply ran the spring over the top of the link arm (which rests on the G# key cup arm).

To make it an even tougher test I laid the sax at the angle shown in the photos rather than stand it upright - and finally, just to make it interesting, I used some old gear oil (I figured the black oil would show up better)...with around twice the viscosity I'd normally recommend.
So, we have a well-fitting pivot screw in a wear-free barrel, a shallow angle and some very heavy oil. At this point I was wondering whether I'd overcooked it, but what the hell - the experiment was set to go and all that was needed was a couple of drops of oil.

The sequence runs left-to-right, top to bottom.
You can see the oil that's just been applied in the first shot (top left) - and here's the really odd thing...I'd set a timer going, and having applied the oil I turned away briefly to make a note of the time - and when I turned back a few seconds later I saw what you can see top right. In a matter of mere seconds the oil has wicked about a third of the way in from each end. Even more interestingly, the oil on the lower pillar has wicked upwards. This will be due to capillary action - in effect the oil is being sucked into the barrel.
This kind of knackered my test a bit, I'd made plans to operate the G# lever against the clock and take photos at specific intervals so that I could present a posh-looking graph showing ingress of oil against time - and while I was busy cursing and damning, the oil met in the middle of the barrel (lower left).
I felt a bit left out now, so I gave the G# lever a few presses - and about 10 seconds later I noted that the oil had completely filled the barrel. The whole sequence of photos covers barely a couple of minutes.

So what can be deduced from the test?
Well, the most obvious point is that popping a drop of oil at each end of a key barrel is going to result in oil getting where it's supposed to go - even when the odds are stacked against it. Personally I'm quite surprised at the speed of the coverage (and, incidentally, it's even faster if there's a bit of wear in the barrel - I tested that too), as well as the ease with which such a heavy oil wicked into the barrel.
Another interesting outcome is the clear importance of giving the pillars a bit of a wipe-over with a tissue after oiling - even with such a heavy oil you can just see (on the lower pillar) where it's starting to make its way down the pillar.
A certain amount of oil seems to remain in a 'pool' around the ends of the key barrel. Some of this eventually migrates away down the pillar (which is why you need to re-oil the action from time to time), but equally some of it gets sucked back into the barrel as the key is operated.

For most readers with a slightly geeky predilection, this is all you need to know - and at this point you should turn your computer off and go do some practice (or have a beer or three).
For the advanced nerds, however, there's more...

With the oil inside a see-through barrel I was able to observe how it moved about when the key was pressed. In both cases (with the tight and loose barrels) it was plain to see that the flex of the key barrel (and there will always be some) acts like a pump, distributing oil around and along the barrel. What was most revealing was that the pivot screw is not fully lubricated all of the time.
For example, as this particular key is pushed down the barrel flexes and oil is pushed away from the upper rear surface of the pivot. As the key is released the barrel relaxes and oil is sucked back in to the void. The effect is just as noticeable on a worn barrel - but rather surprisingly the amount of unlubricated surface area is less, due to the less-effective pumping action as a result of the wear in the barrel. There seems to be a 'break-point' though...a small amount of free play seems to increase the pumping action, but once it gets beyond a certain point it allows to oil to slosh around more liberally. It's also the case that the harder you press the keys, the stronger the pumping action - so heavy-handed players should perhaps oil the action more frequently.
Furthermore, the areas affected by the tension of the spring when the key is at rest (the point where the tip of the spring acts against the barrel and the end of the key nearest the mounting point of the spring) are more-or-less devoid of oil.

This phenomenon was more evident with a thinner oil. Here I've mixed some black oil with a bit of typically thin shop-bought key oil. The pumping action was rather more rapid and widespread, and there was far less evidence of the pooling effect at the end of the key barrels. In short, the oil was simply being ejected from the key barrel.

As you can see on the left here, with the key at rest (top) there is complete coverage of the pivot screw by the thin oil - but as soon as the key is pressed, the oil is pushed away from the rear of the key over almost the entire length of the barrel. This effect is less widespread with a thicker oil.

This caused me to wonder whether grease would be a far better lubricant, so I tried it - and it is...but not for long.
The same pumping action is in evidence - though rather than being a fluid (ho ho) action it's more of an accumulative one. It seems to be unequal too - there's clearly a stronger pushing force than there is a suction one, which means that once the grease has been pushed away from a particular area, it doesn't get sucked back. In short, the pivot screw has to 'wait' until such time as the grease is pushed into an adjacent space - at which point it might then get pushed into the dry spot. And then the cycle repeats. It has little or none of the 'recovery flow' patterns that oil has - whereby it flows into dry spot when the key is at rest - and from a purely observational perspective it's apparent that a greased pivot screw has more dry spots than an oiled one.
One way around this problem is to use thicker, stickier grease -which I tried - but the required stickiness is such that the action of the key is severely affected, and the instrument never gets to the sort of temperatures where a grease would become thin enough to be an effective lubricant.

So what does this all mean?
My feeling is that it's very much a case of "Damned if you do, damned if you don't".
It should at least be very clear that there's some sort of 'peristaltic' action going on, and that stripping an action solely to oil it is arguably a complete waste of time (unless you clean/degrease it at the same time). You simply can't get more oil into a key barrel once it's full, and what determines the distribution of the oil is not how much you put on but how it's pushed around inside the barrel by the pumping action of the key barrel. The two images above demonstrate that clearly - the key was pre-oiled before assembly.

It's clear too that the thicker the lubricant, the more effective it's going to be - but only up to a point. Once it gets too thick it becomes rather less good at its job due to its poor 'recovery' rate - and beyond that it will have a detrimental effect on the speed of the action. It's also very evident that a thin lubricant really isn't much use at all - and that the tighter and more precise the action, the higher the peristaltic pressure will be (though a smaller volume of oil will be shifted - but it will be shifted further, and faster).

To be sure, the stiffness of the barrel plays a major part in the mechanics - but the tubing used for the experiment was pretty stiff stuff, and although I wouldn't expect the effects within a similarly-sized brass key barrel to be as severe, I still wouldn't dismiss the accumulative effects - and once you introduce the slightest amount of wear into the equation the pump-effect ramps up, at least until such times as the wear becomes so great as to negate it.

And so it's easy to conclude that if you want to avoid wear and tear to the action - buy a worn-out horn and slap a load of light grease on it.