What was GM'S intake seal problem?

I have seen many references in this discussion room to GM's intake manifold or gasket sealing failure ohe 60 degree engines.
My 81 year old mother has a '93 Gran Prix with a 3.1, which I've
posted about in here before. As you might guess, at her age she isn't inclined to trade her car in favour of a newer model. She just wants to keep what she's used to from here on out.
The car has performed remarkaly well in terms of never needing any repairs, for about 11 years. However, it recently needed $1400 put into the transmission, and about a year ago another $700 for some new injectors and an ignition module, IIRC.
The car has about 130K miles and so I can't kick too much about the transmission needing overhauled (a drum inside it developed a problem, IIRC, and they just did a complete rebuild).
But I generally wouldn't expect a similar catatrophic failure with the engine, since it's common for most of them last to 200,000 miles and beyond. Hence, I would normally consider keeping this car since the transmission has been redone and meanwhile the engine should still have a lot of life in it -- EXCEPT for the fact that this is an engine design with some kind of inherent sealing problem. Also, I have noticed a vague smell of anti-freeze several times when I enter her garage after she's een driving it, but see nothing visibly wrong under the hood (so far).
1. What specifically is the sealing problem?
2. What engines, years?
3. Are there preventative repairs to be made before hand?
4. What is the typical result of the failure resulting from the manifold sealing design flaw?
5. Any tell-tale signs that's about to happen? TIA
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Most of the time when people are talking about coolant leaks, they are talking about the 3.8 and 3.4 engines. As for your 3.1, and you smelling coolant, the last Grand Prix I had was a 1991, and I could smell coolant but there was never any visible leaks on the ground, or near the engine. One day, during winter, the car ran completely out of coolant, and I wasn't in a position to stop driving, so I continued on to a parts store, driving 120KPH (on the highway), with the temperature gauge red-lined, for around 30 minutes. I got to the parts store, filled it up, and it lasted another 1 or 2 weeks before the engine started to go. We never figured out where the coolant was leaking from until we were pulling the engine out of the car. There is a small plastic coolant hose, on the drivers side, kind of hidden away. It is an "L" shape. This was a few years ago, so I don't recall exactly where it was, but it turned out the plastic had been detoriating over the years, and that's were the coolant was leaking from. The coolant would then burn off on the hot engine, and wouldn't appear on the ground... Basically, if you are smelling coolant, it doesn't necessarily mean it's the engine. Could just be a hose, or the heater core, or many other things, but I would *definitely* get it in to be looked at. Minor problems can turn into major ones if left too long.
Good Luck with the Grand Prix, they are awesome cars when kept in shape!!!

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