The outer chamber oil gets into the Top of the inner chamber - in that little area between the inner chamber and outer chamber.
Any oil 'overfill' in the damper chamber, goes out the little o'ring sealed, brass coloured, sprung valve, on the cartridge - it's about 22mm below the spanner flats of the top of the cartridge.
So, yes, oil can be ejected from the cartridge, into the lubrication chamber. As a bloke who's worked with suspension nearly all my working life, it makes a bit of a mockery of it being a sealed cartridge - the same goes for the more 'normal' cartridges that use a spring behind the compensator piston. I'm just being a grumblebum, I guess. I take my WP forks, and disable that check valve, making it an absolute sealed cartridge, but it means you build / bleed it properly, just like a rear shock. Ho Hum.
It's conceivable that there could be a damper cartridge leak into that small chamber, below the bleed screw, but, as the mechanic found too much oil in the damper (the bladder would have had to be inserted in a compressed state), and the outer chamber was missing oil from std volumes, I'd be Very surprised if that were the case.
Indeed, that check valve I've referred to, would rapidly allow excess oil out of the damper cartridge. A 'rough' rule of thumb, is that damper oil will expand as much as 10% as it heats up, in normal circumstances, hence the reason for check valve / check ports out of the damper chamber.
And, if you had a damper cartridge leaking oil, from any point, it would soon have your forks working very badly.
If the mechanic took the cartridge out of the fork, he could have shown you the bleed valve, and cycled the cartridge through its travel. If any part of the cartridge were leaking, you'd soon see it. If a leak was that severe, that the cartridge could be reduced to an 'open' style, with it being replenished by the compression / extension of the fork, the front ends actions would be rather sub - par. If not, s**t house! You say the forks showed poor performance. - it could be the lack of oil in the outer chamber, increasing the air spring chamber volume, making it too soft, towards the bottom of the travel. It could be a damper problem. If you communicated that to the mechanic, I would have thought he'd check the cartridge thoroughly. For the cartridge to be overfilled, and stay that way, would indicate that somehow, the check valve port was being blocked. If that were the case, your fork cartridge, would hydraulic lock - eg: the fork would not get it's full travel. I've not come across the bleed / check valve being jammed closed ( though quite a few with it stuck open), though.
If he did a full rebuild, I'd be surprised if you have any more problems. Sometimes, if, as a mechanic, you can't find an obvious problem, it's best to go for a 'replace all the service parts approach'.
As I said, a few ml of oil, on a cap /leg/ clamps, can look like a heck of a lot - try the finger drip test. It can't hurt to rotate the upper legs (though any favourite stickers will be askew) so the bleed valve is frontwards, and to also turn the screw out nice and slow, if you are still using the screw.
Mate, your understanding of English / 'Strine, is a hell of a lot better than my Spanish (I've been there a few times, with little more than 'Hola' (sp?) as my vocabulary, and just relying on a big smile, and a relaxed attitude).
