I would have been 10 years old when I first saw it in a theater. In it, Lt. Harris (GW Bailey) is stuck in a traffic jam and commandeers a moped or motorbike and tries to speed through traffic. Someone opens a door to block his path, and he is launched into the air towards a horse trailer. Mahoney (Gutenberg) makes a one-liner joke insinuating that Harris's head has penetrated the rectum of the horse.
That portion still exists in every version of the movie (save maybe some 1980s network television edits for FCC obscenity reasons).
However, I also remember a 1-to-2 second shot of an actual depiction of this. I would expect that some simple animatronic sculptures were used for it (as movies tended to use in the 1980s), supposing of course I didn't just imagine it in my perverted 10 yr old mind.
It's not difficult to imagine why it might have been removed from later videotape and DVD copies, though it's a bit hard to reconcile this even with an R rating.
In general, do some scenes in movies disappear, so much that no evidence can be found on the internet that they ever existed, and in particular is there any evidence that such a scene as this existed and was then purged?