The right rear stoplight on my '84 is being problematic.  I have tried
several different bulbs, bulb grease, cleaning contacts, etc.   The
taillight and directional signal light work correctly and consistently.
I can have the stoplight working after I put everything back together
and screw the light assembly back into the van.  Within days it will
stop working, but as soon as I take things apart, it will start working
again.

What is best solution to this problem?

John