OK, I give up ... been searching the board and the internet with little success

Here's the issue
'93 940 base wagon

Bulb failure indicator in dash came on.

Right rear tail light goes out when brake pedal pressed and R/R stop light does not come on, with ignition in Run. Left rear works normally, center stop light comes on, headlights work normally.

So I put new matching sylvania 1157 bulbs in both tail lights.
Replaced my ground wire from the right tail light common ground bar to the chassis.
Cleaned the metal contact surfaces around the Tail/Stop light socket, and on the socket itself.

No fix.

So I checked the new 1157s, out of the sockets, with my multi-meter - and found continuity between the 2 contacts on the bottom of each bulb.
I thought each filament on an 1157 should be isolated from the other???
(I got continuity between each individual filament contact and the metal base, as I expected.)

Any suggestions?

TIA, Tim

I'm thinking seriously about removing the stop light wire from the right socket, and driving with left & center stop lights.