Oil leak when truck is parked on a hill?

I have a 78 ford truck with a 302 in it and it seems to hold the oil in real good when parked flat drips a little sometimes. Today I parked it on a hill and about 1 1/2 quarts of oil leaked out. Any tips on where and what to look for will be appreciated.Oil leak when truck is parked on a hill?
Oil pan gasket.





Front main seal





Rear main seal.Oil leak when truck is parked on a hill?
probably the oil pan gasket is leaking.
start with the oil filter and the crankcase bolt. If you get under the truck you should be able to see where the oil is coming from!
check the timing seal or the cover gasket.
if it leaks when facing down hill look at the front main crank seal. if it leaks when facing uphill look at the rear main crank seal. sometimes crank seal leaks are tale tale signs of main bearings going out, but if the seal is just dry rotted i wouldnt worry about the bearings.