I'd be pretty irritated if I had my engine replaced and was leaking at the rear main seal.

Oil pan gasket I suck at. I replaced my seal with a new gasket and it leaked as much as it ever did. I'm going to use some RTV next time.
You may want to start there to eliminate it from the leak search.

when looking for a container to hold drained brake fluid, find a container that is different from the beverage you are currently consuming.