Alright i had the block line bored and other machining and i have had a leak since. I have replaced the gasket and the seal 2 times and its leaking again.
Its a 6.0l stroked to a 408 eagle 4.0 crank w/ a stock 5.3l rear main cover.

 

A few things come to mind and will just have to be verified:
1st - anytime a block is align bored, the crankshaft very slightly moves up in the block and the rear seal/cover will need more care in aligning the seal to the crank and not just down to the pan rail.

2nd - If you possibly picked up (p/n 1261566) with housing and seal installed, it could have came with the seal installed backwards. Careful inspection will show that the seal lip is facing outward. Disregard the printed “this side out” on the side of the seal. The lip should be on the inside, or on the reluctor side of the crankshaft. The aftermarket followed the same prints when they developed a replacement. National Seal p/n 100085 and Victor p/n JV1657 are installed in the housing the same way. You need to turn the seal around before installation if you find this is the case.

3rd - Some of the Eagle cranks in the past have had issues with the rear core plug of the crank coming loose and leaking, causing what people think are rear main leaks. You said you have had this issue for awhile, so you may really want to look into this, unless you just know for a fact that it is a leaking seal.

 

Maybe your rear plate not aligned properly? There is a special tool to align it.

 

That's excellent info

 

Where do you get tool???

 

is a core plug not what i think it is/

if it is what i think it is, why would a forged crank have one/

or maybe is it an oil passage plug/

 

It is what you think it it, but in this case the forged crank still has machining performed to it, in which case they rifle drill the mains and when they do, it leaves a hole that has to be plugged.

 

I have a leak somewhere, when I change the flexplate soon I will check the plug. That would be an easy fix. How do you determine that this plug is the definite source of a leak? I mean, I imagine that if the main were leaking there will be oil on the plug, and vice versa.

 

You should be able to tell when you pull the convertor back if the hole in the back of the crank is full of oil. A leak from the main seal wouldn't travel around and into the area behind the snout of the convertor.

Here you can see the core plug in the rear of the crank and in the picture to the left you can see a couple of the main journals where it it has been rifle drilled. This was an LS1 crank.

 

OK, I would have thought it was a threaded plug, but I can't tell what it is. Pressed in? How is it remedied?