this happened to mine and there seemed to be no way to stop the condensation. the only thing i did was i used electrical tape and covered where the bulb plugs into the socket to stop it from rusting. but it only delays it not stops it and eventally they rotted and now no longer work. so i am planing on buying a new set soon.
either take the lens apart then sand/buff the inside OR buy a new headlight...pending how shh Tee looking it is or not then u can put the RTV around the seal......