Originally Posted by upallnight

There are tests to determine if the head gasket is leaking. You can check for combustion gases in the radiator, the kit to perform this test can be brought at some auto parts. There are several Youtube video on how to perform this test.

You can also pressurize the cooling system and see if it holds pressure or leaks out quickly.

Oil on the plugs would indicate that the intake manifold is sucking oil from the crankcase probably due to a blocked ccv valve. Since you do a lot of short distance driving and stop and go driving that is probably the reason why you have the "Mayo" problem.