Hi,
  I recently purchased a 1990 Vanagon GL with manual  transmission.  Around
town and before the van heats up I can shift up and  down to third without
grinding but as soon as I drive on the freeway for any  amount of time and
then downshift or up shift into third it grinds.  I  assume it's because of
the heating up and thinning of the gear oil and a bad 3rd  gear syncro.  Is
this correct?  I assume I am looking at a full  rebuild or replace with a
rebuilt 4spd tranny.  Your help is  appreciated.

Thanks,
David (new owner of Vanagon and love it)