2001 Oldsmobile Alero LEAK

I can use the heater with my A/C running in both modes; normal and MAX. In the midwest, this is sometimes necessary to keep from fogging up the windows and windscreen from the outside due to high humidity. Is there tell-tale signs of leakage on the top of the engine neat the intake manifold? If so, then the intake manifold gasket is blown and requires replacement. This is a common problem with all GM 3.4L V6 engines at about 70,000 miles UNLESS after the first failure, the gasket is replaced with an aftermarket gasket, such as FelPro. The factory gaskets are a common failure point.