Plug the breather. Apply low air pressure through the PCV fitting. If you can put your finger over the air source and stop air flow that will be enough air pressure to work. The leak will show itself quickly. Oil will drip, ooze, stream from the leak area. Easiest way I've ever found oil leaks.
Doug

and you only need about 10# of pressure, if that. start at 5 and see what happens. this is super easy if done on the stand before installation, but perfect for in the car diagnosis as well.

Great idea will try it next time we get a difficult leaker in

Superformance gaskets worked for me; my engine was bone dry last year for the first time ever. Since then, I've developed a few small drips on the floor that I need to check out. In years past, no matter what I did, I always had some slight leak from the get go.

I truly believe that in the future, I'll use nothing but Superformance gaskets for everything. Any time that I've used them, they've just been so much better than anything else. This year, my carb gaskets were switched from standard Holley blues. I've had the carb on and off the car and apart a lot and the things don't stick at all and still look brand new.

FWIW I don't use anything on my oil pan, windage tray, block, etc. Just the spots I mentioned where the timing cover and rear main seal retainer meet the block

Noted!