Its leaking from the rear main area. Not many miles at all, I have a billet rear main seal cap from mancini, or someone like that.

Did I mess something up, or is this common?

pointers, areas of concern.

Chuck over at Lofgren auto specialtys just showed me a new one piece seal that you have to lower the crank a bit, then cut to slide it into the channel, then seal the cut with RTV.
He said they are about $90, but a lot of guys pay more to fix the issue.

I have always run the stock seal retainer. I recently worked on a freinds new 440 with a leak. He had bought a "bilet" retainer. It still leaked. I installed it to the block and measured it up. The bolts didn't even center it in the block register.It was off .100". I had him order a new seal from Greg at
superformanceproducts@yahoo.com
Installed it in the factory retainer, problem solved. I've never had a rear main leak on any of my small or big blocks.
Doug

I agree with Doug, what is really wrong with the factory seal retainer? I've never had a problem either, why reinvent the wheel so to speak.
Russ

1 use stock retainer also never a leak

I have done a half dozen big block builds (all differnt blocks/cranks), always used the stock retainer. Never had or heard of any leaks, some have several thousand miles on them--that's using a felpro seal too. I always put the block surface of a retainer just a touch on the belt sander to even it square---a file could do the trick too, use anerobic sealer between the retainer and block, and squeeze grey RTV in the side seals and I have used those little pipe cleaner thingys. I also offset the seal slightly with a dab of rtv on the ends. Works for me.

I will be looking into the superformance seal for the next build though, I believe it should be a good product from what I have heard.

if block mains were line honed/line bored you may have to remove amount off mating surface where RMS bridge meets engine block.