Dear Vanagoners

My transmission and or clutch is giving me serious problems :
'84, watercooled Wolfsburg edition full camper.

It can be impossible to get into first or reverse.  I will have to
turn it off to get it into gear.

There is a grinding noise that develops when I am at a stand still
with the clutch pressed and in gear.  If I take it out of gear and
release the clutch the sound goes away.  On occasion the sound
becomes a violent shake that moves the van right to left until I get
it out of gear and clutch released.

Question 1:
Any ideas on what is going - transmission, part of transmission, clutch?

Question 2:
Anyone in the Boston/New England US area recommended for dealing with
transmissions/clutches?

Question 3:
What should I expect to pay to get the transmission/clutch replaced?

Thanks,
Michael