Okay, I have one of those little pancake Porter Cable compressors that I bought about 5 years ago as a combo kit. Now it's leaking, and I think it's somewhere up in the compressor head. Normally, the compressor kicks on, charges up to 135 and when it shuts off there's a little hissing sound for a few seconds and it's done. Now, when it charges up, it shuts off, but keeps hissing. The pressure will very slowly drop all the way down to zero if I let it. It's not a huge rush of air, I can barely feel air coming out of the plastic housing up top. It's not the hose between the compressor and tank, it's not the pop-off pressure relief valve (that was my first thought) and it's not the gage/coupling/hose.
I'm hoping there's a valve somewhere stuck open or that needs to be replaced. I'm happy to take it apart and see if I can do it, or take it somewhere. But I don't want to spend a whole lot on the compressor at a shop, if paying someone is more than $75 I'd rather put that towards a newer, bigger compressor.