I had an oil leak that was hard to track, and it too is a very long depressing thread. BUT it was near where you are describing. Anywho, behind the timing belt cover, there are the pullys that drive the cams. Where the cam comes out the front of the head, there is a seal. When I had some work done on my truck, that seal was replaced with a non OEM seal, and it became unseated and leaked down the front of the engine on the driver side, behind the cover. Now, oil can get to funny places with wind, spinning parts, ect, but there may be a chance that the oil could get from the cam, go behind the timing belt cover, and drip around the AC compressor

Like above, it's not a GOO suggestion, but a suggestion none the less! Oil leaks are really frustrating. They also make a UV ADDITIVE that can be added to the oil, and then driven, then when exposed to black light or the expensive uv flashlight they want you to buy, you can track where the oil is coming from
GOOD LUCK