Well I paid $160 for a remanned Bosch starter.  If you really wanna loose   
your mind, try the dealer!

Have you checked the voltage on the battery?  I had similar symptoms.   
 All the lights and the radio worked perfectly but the engine turned   
slowly.  I then called AAA to jump start me and it cranked without a   
problem.  To my undestanding, the starter takes a lot more juice than   
anything else in the van.

Good Luck!

Nate El Great
85 GL-Blue Whale