I have the same problem in my car. Fiddling with the bulb gets it working again. It's been the right brake bulb on a couple of occassions but the rear corners are the big headache. I can clear the warning light by pounding the left corner lens from outside. The right one is infuriating. With the bulb holder assembly in hand, I can move it any which way, shake it, pound on it, and the bulb will stay lit. Once I put the holder into the lens housing, the bulb goes out. Argh!

What I've yet to try is bending the receptacle tangs so they grip the bulb more tightly. I didn't think of dielectric grease. I should try that.

Jeremy, the bulb and tail light contacts look new.

Sixto
87 300D