oil leak...

i put in synthetic oil on my 97 max with 56000 miles before the synthetic it was running dino with no visible leaks. Now i have a leak coming from the oil filter section of the car not from the oil filter itself but from that area. The filter is pretty tight, but seems like the oil is coming from above the oil pan part of the car. Any ideas of where it coming from? My mechanic is having a hard time finding out where its coming from and tolde me to bring it back next week. Also can i go back to regular dino oil after i went synthetic? the synthetic oil has only been on the engine for about 2 weeks. thanks!