Yes. Surely "mud and crap" could cause binding and also destroy the integrity of the collar on which the TO bearing and sleeve slide upon. Although I haven't installed a clutch in a while, Sachs was one of my favs so the "no engage, sometimes slips" most likely are external ailments to the clutch assy.
The tough engage issue could be due to the pilot bearing snagging the input shaft giving it enough motion to prevent successful synchro/hub engagement.
The slipping could well be in the release bearing travel resistance.
These are merely suggestions, proper diagnosis is tough without personal examination. Just tryin t'help.