A new gasket sealed mine up nicely. The only place I get a little bit in is around the passenger side taillight gasket. I've been too busy to replace those.
Can you tell where it is leaking? You may be able to adjust the trunk lid 'tilt' a bit if it is leaking near the top. The taillight gaskets are prone to leaks when they dry out. If you have water near the rear of the trunk, it may be those and not the lid seal.
I used to be indecisive. Now I'm not sure. I feel like I am diagonally parked in a parallel universe. 1968 400 convertible (Scarlet) 1976 T/A - 455 LE (No Burt) 1976 T/A New baby, starting full restoration. 1968 350 - 4 speed 'vert - 400 clone (the Beast!) 1968 350 convertible - Wife's car now- 400 clone (Aleutian Blue) (Blue Angel) 2008 Durango - DD 2008 GXP - New one from NH is AWESOME! 2017 Durango Citadel - Modern is nice! HEMI is amazing! 1998 Silverado Z71 - Father-daughter project 1968 400 coupe - R/A clone (Blue Pearl) (sold) 1967 326 convertible - Sold 1980 T/A SE Bandit - Sold