I used black RTV when I replaced my flanges with SS (the old style {94 and older} are NLA in poly 8 screw).
Did a bunch of reading and RTV was recommended a great deal. The idea being that 5200 is TOO permanent. The factory used some sort of clear silicone product.
Bunch of scraping with plastic putty knife and so on to get a clean surface to bolt the new flanges to the hull.
No issues with water leaking from flange area after all of that work.
YMMV.
Old, bad flange:
