Bravo transom mounting?
 

I am installing new transom mounts, Do you use any sealer, or just the o-ring in the unit?

Usually you don't, but if you want you can put a thin layer of 5200 on the oring(hope you don't to take it back off later).

I just put some below the water silicone on to aid incase of an inperfection on the O ring.

I've installed two Bravo gimbles that way with no problem.

DAVE