4kq, slipping clutch :(

[Robert M]

   Greetings, all!  Been gone for a while, facilitated in no small amount by 
the fact that my 100k mi '87 4kq had been operating almost perfectly.  *Had* 
been.

  Today I noticed bad clutch slipping in 4th gear; it's repeatable.


   This seems like low mileage for the clutch to fail.  Is there anything 
other than a worn pressure plate/clutch disc than can cause a slipping 
clutch?  No evidence of fluid leakage into the bellhousing that I can see... 
  Car shifts fine, though the clutch pedal doesn't always return to the top 
of it's travel.

   I just had the car in the air this past weekend- worked some stiffness 
out of the center diff lock, topped off the tranny fluid, and messed with 
the driveshaft (checking the support bearing and the u-joint; no issues.)


   Assuming that I need a clutch, how immediate is this need?  Will the 
failure progress slowly, will I suddenly have no clutch at all?

  Thanks!
Robert
Ferndale, Michigan