Originally Posted by Tobycatz
... In my research Decosse mentioned that he has seen this scenerio before ...
No sure whether yours is same or not:
Mine ended up being the o-ring on the end of the selector shaft that you can see behind the sprocket cover (I don't mean the gear changer shaft, to which the pedal is attached - the shaft that goes through the selectors)
Item 15 on item 16.
possible to replace that o-ring without breaking cases but you must be VERY
After you remove the retainer, you can pull the shaft out towards you - but as the o-ring releases the shaft will want to come with a rush!!! So make sure you have some stop mechanism to avoid pulling it out too far. Similarly, when putting it back in, you must be equally careful not to insert too far - same thing will want to happen, that you press in past the resistance of o-ring and it will go home flush before you know it (which you DO not want!!!) Ask me how I know.
A pair of vice-grips locked onto end of shaft will prevent this. Rotating ('screwing') rather than direct push is better/safer technique.
Even after replacing o-ring a couple of times (thought I had maybe nicked it while installing) I still had the leak. Ended up withdrawing it again, putting some sealant over the shaft and re-installed and allowed to cure. Hasn't leaked since.