It really has nothing to do with heat and riding longer- , and greater distances....
The cause is that the gasket only closes the outhern ridge of the transmission , and not the inner ridges of the area where the actuator is located.
So every time when the clutch lever will be released , it sucks a little bit transmission oil through the very thin openings between the ribbons which are not covered by that too simple made gasket ( when there is no vent installed to abolish that "balloon pump" side effect )
The most easy way to press that collected oil away again , is not through the tiny openings called above, ...but through the hollow main shaft .
The reason that one M8 suffers more of that side effect than the other M8 , is probably due to little differences of the thickness of the gaskets or wee differences of the moulded inner reinforcement edges of the inner covers. ( I don't know ,...I never could have measured such differences of course )
( My question also was : Are there any differences between the inner cover of a TC - , and the inner cover of an M8 equipped with hydraulic clutches ? )
Luckily it's all resolved now ,....and translated from Dutch language we say "It's just mustard after the meal now"


Watch this ( and see what happens 5 minutes later from the start )
You will see an amount of collected ( sucked in ) transmission oil coming out , as soon the actuator was just removed.