The distributor is on the opposite of the engine to the timing belt - so it is very unlikely that replacing the distributor oring will fix this problem. A leak from the transmission pan gasket also would not contribute to oil dripping from under the timing belt cover. The valve cover gasket is a possibility, but it wouldn't be my first choice.
If you have oil leaking from behind the timing belt cover, IMO, it is probably your oil pump gasket or your cranshaft oil seal in that order. It seems that the oil pump gasket leak is a common problem on the GEN3 Camry. Normally the oil pump gasket and sometimes the crankshaft seal is changed at the same time as the timing belt. That is why Stillrunning asked the question about when you last changed the timing belt.
On my '96 Camry, I had 2-3 oil drops per day leaking onto the driveway when I changed my timing belt and oil pump gasket. The area behind the timing belt was an oily mess. Click on this link
DIY: GEN3 Timing Belt + Waterpump + Oil Seal Change - Part 1
and scroll down to Step 25 to see what the area behind the timing vover looked like on my car. Then scroll down to step 39 to see what the oil pump gasket looks like. Teh gasket is only $19, but it is a pain to get at it.
If you click on this link
DIY: GEN3 Timing Belt + Waterpump + Oil Seal Change - Part 2
and scroll down to step 43, you will see what the crankshaft oil seal looks like. Only a $10 part, but also a pain to get at.
My guess is that it is one of these two seals.