I had the same exact brake light problem after replacing the lens assembly in my v90. The easy fix is to go slam the trunk a few times. That would fix mine for a few days. Now if you want to know what is really causing the problem, it's the metal contacts on the plastic mount that fit into the taillight assembly. One of them is not making touching the metal that it's supposed to be touching. I took the little plastic mount out, cleaned the metal (on both the bulb assembly and the lens assembly) and bent each contact slightly outward so that it was guaranteed to touch when reinstalled. Never had the problem since.