Best way to fix this common problem is to unscrew ALL of the nuts holding the lenses in. Disconnect the wire harness (leaving the bulbs inside the housing). Then, warm up the surrounding lens edges with a hair dryer or heat gun.Do one section at a time. BE CARFUL NOT TO MELT THE HOUSING.
The black butyl will soften and CAREFULLY rock the lens back and forth until it frees itself.
Clean up ALL of the old butyl using thinner. BE CAREFUL NOT TO LET IT LINGER ON THE PLASTIC LENS.
Reseal the lens housing on the outside with a silicone sealer and let dry.
Re-tape the body (taillight housing section) of the car with NEW black butyl.
Reinsert the lens sections one at a time and refit all nuts.
Conect the wire harness.
YOUR DONE!