Interesting, I have never seen a tail light socket fall out of any of my 'birds. (around 15 or so, times six bulbs = 90 sockets)
On rare occasion one will pop loose, but I've never seen them fall out. They are generally VERY tight to remove.
Either the housings have been ground out, or the wrong size or type of socket must be going in. I always use original sockets, so I can't comment on any replacement ones. And yes, the socket needs to ground to the housing to keep all the electrical gremlins out of your car.
Is it only a few that fall out, or all of them? Any way to measure or compare differences to the ones that are not falling out?
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