If the tail light mounting area is the correct shape, you should not need any sealant on the backing plates.

Each backing plate is retained by 2 small sheet metal screws via 2 holes in the body. It is important that at least 1 of the 2 screws makes a good ground for the tail lights.

Then the lens is attached to the backing plate with 2 unequal length machines screws.

I hate to say this, but if there was any damage to the rear, the lights should have been test fit before painting.

I know it is a pain to test fit, but you get better results if you do. I have seen more than 1 car that had to be repainted because of similar problems, mostly Volvo 1800 where the front chrome grille surround meets the body.

I can't tell you how many times I have seen a crappy fit for the front surround on 1800 and all because the piece was not test fit before the car was painted.

Can you supply any pictures?
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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502