I had to use a sealant on the flange between valve and heater core. I used
Yamabond 4 because I had some and know it's a good product. My first
attempt failed because I didn't let it cure long enough (24 hours). After
curing for several days I put the core into service and verified that it no
longer leaks. I don't know why I had to use sealant, I've never used
sealant before and have not had leaks.

-Mark

On Tue, Jan 18, 2022 at 6:13 AM Mark McCulley <markmcculley@gmail.com>
wrote:

> 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
>