Although I don't know if it is a language barrier, mistake, or if you are not aware.. The fluid in the hydraulic clutch system is mineral oil. If this is a misconception on your part, I'm sure you must realize the difference in lubricity between mineral oil, and hydraulic fluid in that environment..
I find your theory about the way such a leak would end up in the engine case interesting, and worhty of consideration.
I did fail to mention that I was having clutch engagement/ disengagement issues over a period of months before my failure happened. Flushing the system of old fluid, and bleeding it "seemed" to cure the problem (had to do 2 or 3 times in those 5 or so months preceeding the failure).
My theory could certainly be flawed, it wouldn't be the first time.