Hi Folks

I drive a 84 vanagon with close to 200k miles.
For the last 100k miles, every once inwhile
it would experience a tranny-crisis as follows:

from dead stop
in first gear
barely start creeping forward and....

        BAM!  There'd be a sharp noise, the tranny
        would pop out of gear, and it felt like
        I'd been bumped into from behind.

        I'd shift back into first and away I'd go.

Yesterday, while 200 miles from home, this happened
again, only I could not get it to engage first
gear.  If I try, I hear unusual spinning sounds from
the tranny and there is no forward thrust.

When I described the earlier symptoms,
a guy at a local tranny shop said "o, your synchros
are bad.  It'll be $400-600 if you pull and reinstall
the tranny."

Question: What do you think of this diagnosis?
Is it really "my synchros"?  I've done the clutch
how much harder is that?  What do rebuilt trannies
run?  Junkyard trannies?

Other option....
anyone interested in buying my van from where
it sits in Traverse City Michigan?  Body is in great
shape.  Former passenger bus, custom camper.  Propane
furnace, roof vent with fan.

Steve E
East Lansing Michigan