Porter Cable Compressor Problem

I'm new to this forum so I hope I am posting this to the right place. I have a Porter Cable 6 gallon air compressor for the usual small air tools. I had it for about 3 years now. It developed a leak. I could hear air coming from under the plastic housing, so I took the housing off and found the leak coming from the compressor head. There is a depression cast into the head about 1 inch deep. At the bottom of that depression there is a metal bottom about 3/16 diameter. In that metal bottom, I found a small pinhole. I could cover the hole with the tip of a fine pencil lead (.5mm) and the leak stopped, so I'm sure I found the source of the leak.

What is that hole and metal bottom for? I assume it is the air intake for the compressor, or maybe it is a relief valve of some sort. Do I need to take this thing into a "certified repair center" or can I fix it myself? The head assembly doesn't look all that complicated to work on, but I don't know what will happen when I start removing screws...I hate when I hear "boing" and have to spend the rest of the day looking for springs and other parts. The compressor still works, for now, but I don't think it will fix itself and will only get worse over time. Eventually it won't hold air at all.

Any help from out there would be appreciated.

in the head. The function of an unloader is to vent the compressed air in the cylinder and line to the tank so the piston isn't starting against pressure. There's typically a check valve just before the tank. My unloader is in that line but was originally in the (cheap crappy) pressure switch assembly. Mine does have a small hole like you're describing. It goes "psssh" when the compressor shuts off. I've had mine stick open before so it vented air when the compressor started. The fix was just to rap it with a piece of wood :p.

Thanks. You may be right. I do remember a small hiss when the compressor stopped. Now it doesn't stop. The line from the compressor ends at a brass fitting on the tank. That fitting must be the check valve. My problem isn't with that hole (which is supposed to be there) but with the check valve. If it is leaking through it is keeping the whole compressor charged until all of the air leaks out.

Now, I need to figure out how to fix the check valve. Next time it runs and leaks, I will try whacking it with something. I may need to get that valve replaced.

Thanks for the help.