Florian Speier wrote:
> so do the heater cores typically go bad at all? am I safe just replacing the
> valve?

The rear cores are infamous for going bad.  That said, here's my experience:

My '84 7 passenger had the same problem as you.  I replaced just the
"O-Ring", in about 2001, and it's still not leaking.

When I got my '85 Westy, in 2002, the rear heater had been bypassed by
the PO.  The core had telltale signs of leakage and, sure enough, it was
bad.  I replaced the core and O-ring and it's been fine (and used often)
ever since.

You know what they say, though ... YMMV.

Mike