My wife's 99 GC has always had issues with the right side tail light. In particular the turn signal bulb would stop functioning. The bulb was not blown nor was the fuse. I would simply need to jiggle the bulb socket a little and it would work fine for a few months and then stop working again.
The other day I noticed the rear parking light on the right side was out. I pulled the housing and found that the plastic supporting the light bulb socket had melted. As a result one of the metal tabs that makes contact with the bulb socket was loose. I used an epoxy putty to rebuild the housing around the bulb socket. However, I thought about what could have caused the plastic to heat up to the point of melting. After a beer or two I thought about arcing. I noticed that there were indentions on the metal tabs of the housing where the socket rests... almost like wear spots. So I decided to use electrical solder over these indentions thinking that this would ensure good contact between the housing and bulb socket. It appears that the bulbs are now working as normal. I hypothesize that the tabs on the bulb sockets wore into the metal tabs on the housing enough to cause arcing. This generated the heat that caused the plastic to melt. This is also the reason that my turn signal bulb kept failing. Hopefully this is a permanent cure. I've attached some pics in the hopes that this may help others. If I'm wrong I blame it on the beer I'm drinking right now. Please notice the yellow circle around the wear spots I mentioned.