The inoperative right brake light is working again. After cleaning and tightening the ground, checking the fuse, cleaning the circuit board connection, and replacing both left and right side bulbs, I replaced the 9 month old bulb warning relay with a used one from the junkyard. The BWR fixed the problem.
It is discouraging that the relay failed after only 9 months (9 months ago all three brake lights were out). Can they be repaired? What to look for? Who fixes these kind of units, or am I stuck with just purchasing another new unit? I have 3 volvos that use these things, and given their poor reliability, I'm looking for a cheaper alternative than new purchases. Thanks for any advice.