[floatingkiwi]

Yep, do what harvey says.
I had the same problem on a 92 JDM. In fact the rear light cluster seal doesn't seem to do a marvellous job when it gets old. ALSO you may find the steel surface under the seal surface might be slightly too far towards the front of the car (hence not mating too well with the seal). Seems to be from the spot welding done during manufacture.

Take off your old seals, tap that seal surface flat (with wooden block only) apply a wee bit of sliastic and put 'er all back together and not only will your lights not fog up but your boot will stay free of water!! (if you are unlucky enough to have that problem as well)

Matt