Can't imagine where engine oil could be coming from in that location, especially since they replaced the pan gasket. Fluorescent additive that Kent Moore sells can be added to the engine oil with no problems, and can be left in till your next oil change, so I imagine it's the same stuff the auto supplies sell but at a much better price. I would wash it off as good as possible, add the dye to the engine oil, then run enough miles to start the leak again, then a black light should show a trail right to where it's coming from, if not then it's not engine oil. I'm surprised the dealership didn't do it to verify the source of the leak before replacing the pan gasket.