I am replacing my TRS with a fresh drive and think it's a good idea to flush the reservoir on the transom assembly. The reservoir cover seal is discontinued. Does anyone know what it is made of before I pull it apart and destroy it?

Unable to say, but what about remove the assembly, dump it out, then put some diesel in, shake and dump again. Repeat till its clean

Felpro makes sheets of gasket material . It comes in a package with 4 sheets that are used for different fluids. The part # is 3060

Dow 732 RTV will work just fine. Just make sure surfaces are completely clean & dry