Andy, try cleaning the bulb socket and the mating area on the body. What you are discribing is a loose ground and the bulb is finding it ground thru the right sides bulbs, thats why they are extra bright too.
My taillight harness is brand new so there is no corrosion anywhere. All connections are bright and shiny. I can check voltage drop with the lights again but so far I haven't noticed any difference from side to side.
