Compliments of N*caddyI gone mine off ebay for my Deville, and I did need to reuse the rubber "grommet" that was on the old one that 'secures' the antenna when it goes through the hole in the body.
I think i also saw a post here on this site on how to rebuild the power antenna yourself, only after i bought a replacement.
The bracket that attaches it to the frame would also be different. My replacement unit bracket did not match but it just unbolts.All mid to late '80 up into the mid '00 power antennas equipping GM vehicles are the same apart from the rubber grommet (witch is specific to the car's body shape). You may find that a Chevy power antenna is less than a Cadillac power antenna. It is essentially the same part just aimed to different buyers.