I had the same seal you're talking about on my Z11. It was an NOS GM seal that tilted inwards instead of folding outwards. I was harassed all the time by poeple telling me it was upside down. I would even take it off and show them the mounting flange on the bottom to prove it was mounted correctly. I believe the problem was that GM went to a newer version of the seal in recent years that was markedly different than the original style.
https://www.yenko.net/ubbthreads/show...8/fpart/1/vc/1