These are all known issues, on a viriety, actually 75% of all makes and models by this leader in the technology of moving people......s wallets!
There are so many TSB's and so many variences of them based on what you paid, baught and so on. The warrenty team is a real treat to deal with. Straight fact is that it is a very poor design, maybe intentional to provide after sales revenue, only the shareholders know.
It is usually around the intake manifold that the gasket fails and no where near what type of mileage you should get from such a long respected manufacturer who knows better.
The engine series is now in a variety of lines, Impala, Grand Am, Grand Prix, Bonneville, Monte Carlo....the list goes on.