How to know if Main seal (Back Seal is leaking?!)

Hi guys, my cars has a damn hard oil leak to find, Sometimes I think its coming from around the oil Sump pan, then sometimes I think the engine Main seal behind the fly wheel is leaking, Please give me some professional advice on locating oil leaks from under the car? I usually degrease everything, make sure its all clean, then start the car and let it run a while, rev it a bit, then try to see where its leaking, but this car has a sense of humor, WHen its jacked up and leaning back for me to try to see where its coming from, it doesnt leak anywhere I can see, when i put the car down flat, drive it a bit and come back..then oil is all over, I cant tell where its coming from, help? :\
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jack the car up high, put some blocks/bricks under the wheels, then jack rear and do the same.
car is still level but alot higher and you can still see under it to see where it leaks from.


another option (not easy one), but if you are unsure, then take it apart and change the seals for peace of mind.

i did that when i had my last engine in the car, i was unsure where it was leaking from so i just changed it, leak stopped.. lol