I've been hearing what sounded like an air leak for quite a while but couldn't find it, well today it got bad, STILL couldn't find it, I thought maybe a fitting, sprayed them all and, nope not there, perhaps a bad piston wring, nope, no air out of the breather, then perhaps the pressure gauge, I had a spare so replaced it, hooked up my tank opened and was checking the gauge and just happened to see the back side of the right filter, there was the o-ring poking out. Now, those that haven't had the joy of working on them, they, at least mine, are HARD to get apart, I removed the top connector tube then beat the poop out of the top cap with a Ford wrench on back wards and a heavy mallet, end finally came loose, got it off and the 0-ring was definitely messed up, luckily in the parts kit were 4 spares. I see how it got messed up, they put the 0-ring in the top of the tube then threaded in the end piece, shredding it. I greased it up, and the threads, put the 0-ring on the cap and screwed in the cap as as it was making contact kept working it in slowly in - out, in-out to make sure the 0-ring would seat. The foam filter had moisture on the top but was only discolored half way, replaced it anyway, had a spare for that too. Tried to take the Left one apart and that wasn't happening so I gave up. Got it reassembled, pressurized it and no leaking. Fired up the compressor and refilled my tank, YEA!!!!! went faster with no leaks. I've got about 25 hrs on this unit