I just replaced a leaky rear heater core and am having an issue with the
flange on the new core sealing to the metal GoWesty valve that I've had for
several years. I did obtain and use a new o-ring from GW. It seems that the
new o-ring isn't compressing sufficiently--the plastic flange on the heater
core bows in the middle when I cinch down the two bolts that secure it to
the valve.

Has anyone else encountered this problem?

-Mark
'87 Westy