Help with an oil leak

I have a 97 Grand Prix GTP, and for some time now I have had a slow oil leak (I usually have to add 1 quart between oil changes). The leak is somewhere on the passenger side, as oil gets onto the main drive belt and gets dispersed all over the passenger side of the engine compartment. I have replaced both valve cover gaskets, as well as the intake manifold gasket. It would be greatly appreciated if someone could point me in the right direction for this. Could it be from the oil pan gasket, the oil sending unit, or the oil filter adapter if it is getting onto the main drive belt? Thank you

Take a look at the oil filter adapter where it bolts to the block. i think these are troublesom on the 3800's.

Since oil is getting all over the main serpentine drive belt check the timing cover gasket and crankshaft seal behind the harmonic balancer. Also, the oil pan gasket can cause a similar issue. Safely jack up the car, remove the passenger side wheel and the plastic splash guard in the way and do a closer inspection.