SCAT 408 stroker crankshaft rear main seal leak

I have a 408 I built last fall using a SCAT stroker kit. No rear main leak when I first ran it but starting leaking after a while and continued getting worse. Replaced the rear main about a month ago - worked great for a few weeks but starting to leak again. Used a standard Fel-Pro rubber rear main set both times.

Anybody else had this problem or have any suggestions to get it fixed for good?

Thanks