I have been thinking about your hot slipping clutch ... (Oh baby!)
To the serious side and I don't think it has to do with the hydraulics.
Here are my thoughts: At rest, the clutch master/slave system should not ideally influence the clutch assembly at all. That is where the questions of free play comes in. I would still like to know the amount of free-play cold and when it slips.
My thoughts continued- if the inlet port was not being uncovered fully and thus the piston is not getting a full stroke and replenished, this would show up when using/pushing on the clutch pedal. You reported slipping when your foot is off the pedal.
This leads me to the thoughts regarding-
- the difference between when it does and does not slip. You say it slips after considerable amount of driving (time to heat up)
- the take-up (engagement point) is high off the floor. This is commonly associated with a worn clutch disk OR a bad pivot ball/clutch arm inside the bell housing.
-you said that the clutch disk thickness measures within spec, but because the measurement is at the slave cylinder and its amount of extension, a worn clutch arm pivot ball could give you a false reading.
-a failed clutch arm would also do this, but it seems very unlikely that the arm itself would fail. I have no experience to share with this part or its life/failure.
When you were under the car measuring your clutch thickness, did you get a chance to see if there was excessive movement of the clutch arm? This might be a telltale indicator of a pivot failure.
Unfortunately, I believe access to the pivot is the same as doing a clutch and once you are in there, might as well do it all.
Like you, I am hoping that the clutch disk is thick and happy, thus not needing any major work.
I could be off base on all this, but I continue to think about what is going on with your slipping hot clutch!
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)