Here is what works.  Yes, clean all the electrical connections in the
starter circuit.  More importantly, invest in the Bosch WR-1 starter relay.
 Get from list vendors.  This relay puts full battery voltage on the
starter solenoid.  Before I put the WR-1 on, even a relatively new starter
and a new ignition switch wouldn't cut it on a hot day.  Now at 100+F and
everything super hot, van starts like a champ.

John Lauterbach
'84 7-passenger
Macon, GA