Just went through this myself.. I "had" a 440 source retainer on my 520 stroker. It leaked bad. I tried all the suggestions on here. Indexed seal halves in different spots, rtv in all the right places, main stud clearance, cut a oil drain path in the retainer. Still leaked. I took that thing off and tossed it in my scrap pile. I pulled out an old crusty factory 400 retainer, cleaned it up put it in and no leaks. I called Jim Hale up and he told me he never had any luck with those billet pieces..