My car has a 305TBI and auto trans (I know, I know........... ). When the car is cold and just sitting there, it doesn't leak a drop. When it's running or right after it's been running, it leaks a fair amount of oil from the back of the motor. It runs down off the trans pan and that black plastic cover between the trans and the back of the motor. The oil pan gasket and valve cover gaskets are new, and from what I can tell it's not coming from either of those. I also can't find anything from the top or front of the motor. Any ideas what it could be?

It could be the intake manifold (rear China wall) gasket/sealant that's leaking, or the rear main seal, or the oil galley plugs, or the oil filter, or the oil filter adapter, or the distributor gasket, or the oil press sending unit, or the dipstick, or oil press switch near filter.
(not sure if TBI cars have the last one)

Need to clean the area as well as possible, get a strong light, crawl under the car and look for it. Brake cleaner (in a spray can) does a pretty good job of cleaning off the old oil.