My Halloween psychic powers tell me there's a coil conversion in your future.
Take a deep breath. Take a step back for an hour or two. Drink a beer or three.
The leak could be very, very small, and it could be in the valve block which you are about to rebuild. Don't fret, order the new compressor seal and o-ring kit, and knock out those two first. They're cheap and easy. Take it from there if you still have a problem. Before too long, you won't be able to find any leaks, because your compressor is going to completely stop working. Fix the things you know are bad first. And have a beer. And a milky way...it's halloween.