I've been following this "silver secret" discussion for a while now -- any 
chance this is related to the dash socket for a collapsible spare tire pump? 
My '74 Westy came with a collapsible spare that fit under the sink 
compartment, and was (according to the owner's manual) supposed to come 
with an air pump that plugged into a little silver socket on the dash.  When I 
bought the bus, the spare was there, the socket was there, but the pump 
was missing. 

Just a thought. 

--Dale