I have found the culprit.
The little fan motor is indeed the problem.
The nylon top moulding is corroded, probably by the soldering flux, and the
positive brush fell out of place and touched the case of the motor.   I have
never seen corroded nylon before!
It has probably hardly ever operated but its 16 years of age took its toll.
Nothing for it but to replace it.
Thanks for your tips group, especially David Beierl.
Taking the fridge out was straightforward with the exception of the flue vent
and that broke out a piece of plastic lining of the van which should make it
easy to get back in.  All I have to do now is replace the fan with another.
What a nice community!
Steve Cotsford
'84 Westy
Columbia SC