99 Grand Prix intake manifold question

My 20 year old son has just bought a 99 Grand Prix, 65,000 miles on the 3100 motor. He did not take my advise to have the car checked by a mechanic. After a week he complains
of no heat, so I check the radiator and lo and behold there is a shit load of stop leak in the system. I could check before he bought it because he was in a HURRY. The really bad thing is that his Grandfather pick this up at an auto auction and he never checked it before or after he bought the car( he trys to run a used car lot at his body shop). We flushed the system as best we could so he now has heat but we now wonder why this crap was put in there? I'm sure it isn't good. He took the car to get the oil changed and the shop said it needed intake gaskets. A friend of mine says it can't be that because there are no water jackets in the intake. I'm a bodyman and know little or nothing about mechanics. So, is it possible that its the intake or are we looking at a head and or head gasket problem. Thanks for any opinions,
Kirk
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Intake gaskets on that engine have been and still are a chronic problem, if there is coolant in the oil or an external leak around the mating surface, it is the usual int. gasket. Gm has an updated gasket set that should be used, thorough flush of the cooling system if it is sludged up is also critical. If there is a coolant oil intermix, be careful with engine bearings, you don't know how long it was run this way.

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There doesn't seem to be coolant in the oil but leakage around the mating surfaces like you said. We are going to take it to a mechanic that we use to look at it.
Kirk

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Pull the oil filler cap, ,and look for the brown milky sludge too. Also look for sludge in the overflow tank. When my 00 V6 intake went, those were the symptoms, as well as the leakage that you described. Get the gasket from the DEALER. NAPA or Autozone does not yet have the correct upgraded version. For an extra $15 or so, replace the overflow tank too (if is is contaminated) You should be able to tell without a doubt if there is crap in there.

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