the round viton seal doesn`t need sealer but there are fiber seals up the sides of the seal plate ,these can be very hard to get sealded up properly . I use right stuff sealant up both sides & then pack in some sealer along the gap with a small screw driver from inside the crankcase .
the new Fel Pro seal has pipe cleaners instead of the fiber strips , I still have not figured out how to make the pipe cleaner strips work