Definitive way to make sure fuel pump diaphragm is bad?

Just curious. I drained my oil a while ago to repair my rear main seal issue (didn't fix it by the way) and the oil had an aroma of gasoline and was definitely dirtier/browner than it should have been. The engine only had a couple of hours of run time on it and zero miles on the road.

Is there a proof-positive way of knowing if the diaphragm is my fuel pump is leaking fuel into the crank case? Or is this just something that one "guesses" at? If it's of any help, the fuel filter that sits on my manifold and feeds the carb fills up momentarily and then quickly goes to looking empty, although the engine will continue to run.

Stock fuel pumps are cheap. If the oil smells like fuel, change it - the oil too.

You could find out like I did on my 65 Cuda, the crankcase ended up with about 4 extra quarts of gas. Wondered why it kept stalling out on me

What type of pump is it?
Some can be disassembled, inspected, and rebuilt.