97 Lumina oil leak

My Lumina is developing a minor oil leak that is showing up on the side of the oil pan directly above the drain plug. The ridge at the top of the pan looks wet and oil appears to be running down from somewhere above that. Can someone suggest where this might becoming from? There's 101k miles on the car and the lower intake manifold gasket/oil pump seal o ring were replaced at 35k miles. Thanks.

It's not impossible that the o-ring could be leaking again after 80k since changing it. The other suspect could be an oil pan gasket leaking.

Thanks.

I did find 2 leaks -the oil pan bolts near the front of the engine were loose and dripping oil down to the engine mount bracket and to the bottom of the oil pan. I tightened two bolts and that leak stopped. I now see a second leak which is really only a smear of oil about the size of a quarter on the bottom of the pan below the rear of the engine. It shows up only after the car has been off for a couple of days. It looks like its coming from a seam or a weld between the bottom and side of the pan. Is this possible? I'm not familiar the construction of the pan. Thanks.