I have been working on an O-320 that has had a high oil temp (red line high) problem for years. changed cooler, modified cowling. new oil pump for AD, temporarily installed a second oil cooler, changed the vernatherm 3 times, pulled out lots of hair and finally got it cured.
The oil screen housing that holds the vernatherm was not holding the vern. in the center of the hole in the case, just so slightly off center.
the vern. had a ware mark all the way around the tip but was not sealing the bypass. changed the housing and it cools just like it should.
can see no sign of damage to the old part at all, looks like it was made that way.