I just drove back from a clients place, and I lost my tranny----sort of.

I have an '84 Westy with an auto transmission. I lost reverse gear today,
and now the forward gears are bad.  They chunk and clunk and stutter.  In
fact, when I got home I tried to reverse again but went forward only.  Even
in park and neutral.

Its cold and wet and snowing outside so I have not looked under the van yet
or checked the fluid.  Does this sound like a simple problem, or a known
problem, or do I have a thousand dollar repair on my hands.

If the latter, how hard is it to retro fit a standard tranny on my van?

thanks

Gregor