Cluch Slip

Clutches on any car are not really checkable from outside. Clutch slip can be due to several things including disintegration of the clutch disc. But probably its simply a failure of the ZF input shaft seal- a $3 part at any local bearing supply house. You'll have to remove the ZF with the bell housing attached to be sure. Replacement of the clutch is mandatory if oil is dripping out of the bellhousing bottom, or if the disc is badly worn. The ZF weighs 155 lbs and is oily/slippery, so get a couple of friends or rent an engine hoist rather than rupturing yourself.

Thanks Jack.
I adjusted the "slave cylinder control lever" to let the pressure plate close all the way. I guess the normal wear of the disk was not allowing the pressure plate to work correctly. No oil leaks so far (knock on wood).