Unfixable Oil Leak

I just did new main and rod bearings in my 304 with the rest of the engine assembled. Its easy to do. Just look at the shell and see what you have regarding size. These bearings won't help your rear main leak because there isn't that much material added/removed by the bearings.

My thought on the leak is that there may be a requirement to put sealant on the cap itself - have you followed factory manual on rear cap installation?