quite possible that if the input shaft seal on the tranny or your rear main seal fromt he engine was leaking that would get on the clutch disc surface and cause slippage. kinda odd that a relatively new clutch is slipping already... could be a TOB or a clutch pedal freeplay problem too.

the main shaft bearing could be the suspect of all the problems (speed sensor cracked is no biggie, unless you are loosing fluid...this could cause transmission failure). the fatigue of constant clutch dropping/aggressive driving/sliding will destroy the mainshaft bearings pretty quickly in the S chassis. this, in turn, will 'wollow' out the input shaft seal on the tranny and possibly throw gear oil on the clutch friction surface. if you are hearing a whining while the tranny is in nuetral and the clutch is engaged (no foot on pedal), then the whinning dissapears when the clutch pedal is pressed...this is a telltale sign.

i have done this to 2 s13 trannys from aggressive sliding over the years.