Rearmain Leak On New Crate Motor

[Ardee83]

I ordered a brand new 350 crate motor from JEGS. As soon as I finished installing the motor and took it for its first spin, the rear main was leaking. Since it has the 3 year GM warranty I took it into my local Chevy dealership, that was a fight the serviceman was adamant it was impossible for the rear main to be leaking on a brand new motor. I told him I'm 99.9% sure it's the rear main I've had it on a lift and traced the leak it leads back to the rear main. So after a dye test guess what I was right leaking rear main. So they replaced the rear main I drove it for 3 miles and the new rear main is leaking. I called the dealer back let them know the rear main was still leaking, his reply again I don't how it could still be leaking its brand new. My reply ya I know and so was the rear main when I got it. So to make the long story short the dealer was unwilling to replace the rear main again. So I have decided to drive 15 miles to another chevy dealership I made them aware of the situation with the other dealership and have asked them to replace the rear main for a second time and to ensure that it is repaired and if not to keep the truck until they discover the issue that is causing the rear main to leak. So my question for you guys what could be a possible underlying source causing oil to leak from the rear main? All possible scenarios are welcome. Has anyone ever had a crate motor replaced with a new crate motor?

Installed in an 83 Chevy C10 2WD