I had sent a thread out several months ago regarding my 1970Z28. New one-piece performance gasket from fel-pro with a new milodon oil pan and plenty of RVT Black Silicone and guess what?? About the time the motor gets up to temperature, 20 minutes or so after starting it, it begins to drip oil between the gasket and the pan at the bottom part of the rear radius below the rear main cap bearing area. I can visually see it being squeezed out from between this area.

Is there anyone who has had this issue with 1 or 4-piece gaskets and what the heck am I to do about fixing this?

Are you sure it's the gasket and not the rear seal??? If this is a 400sbc and has had the mains alignbored or honed,,,,,, you need a special rear seal. You can guess know how I know this!

Marv, I'm glad you chimed in on this one. I'm about to attempt to change the rear main on my 400 to the one you specified. How would one go about getting the upper half out of the engine with the crank still in?

MaTt

It is the LT1 350 engine. The rear main bottom half portion looks brand new. There is absolutely NO oil on the upper part of the bellhousing or flywheel

Matt, it's especially easy if you have the wrong one in there now. Just push it gently and if necessary roll the crank over in the same direction. But that's unlikely, just give it a gentle push and it will pop right out the oither side, just slide it around. Installing the new one is a little more snug, but the same principle.

70z,, if you SURE it's not the rear main,, I'd be inspecting the pan lip and see what's going on. The rear main cap is a fixed diameter, the pan gasket is a fixed thickness, there is only one other place (as far as pan seal) to investigate. But that's if you are SURE the seal is not the issue. It's still my suspect no matter where you find the oil.

70z, there are 2 different thicknesses for the one piece oil pan gasket. Perhaps the one you have is too small.
MaTt