Have to wonder about all the different kinds of equipment on a Westy.
The shut off  valve on the propane tanks in both my 84 and 86 is the
screw in/out type, much like a water tap.  Mine was leaking when it was
screwed all the way in but was fine in the fully open position.  Acting
on advice from a friend who knew what he was about, I dismantled the
valve and spent twenty five cents (Canadian) on a new O-ring.  No more
leak.

Earl