1997 Monte 3.1

I have a 1997 Monte Carlo, 3.1, with 53000 miles. I have a low coolant light on, milky substance on the underside of the oil fill cap, and the oil dip stick has a light brown tinge to it. The coolant is brown sludge, in the radiator and the reservoir. I am thinking head gasket. If this is so, what is a fair price for repair. What else could be possibly be wrong besides head gasket?
Thanks in advance...
Gus

I think you hit the nail on the head (sorry, no pun intended).

Get several esitmates for comparison, it won't be cheap.

The intake gasket leak these engines are infamous for will pump coolant into the oil, so do a compression test and cooling system pressure test before tearing the heads off. An intake job is much simpler and less expensive than a head gasket job.

The intake gasket leak these engines are infamous for will pump coolant into the oil, so do a compression test and cooling system pressure test before tearing the heads off. An intake job is much simpler and less expensive than a head gasket job.
I had the engine looked at by a mechanic, and his diagnosis is the intake manifold gasket as well a O2 sensors. Thanks to all the help.