I've worked for GM dealers for the last 27 years and owned only GM products but it seems that since the mid 1980's their quality has gone downhill. They will use less reliable parts if they can save $2, and when it breaks down after 36,000 miles they issue a service bullitin explaining the way it should have been manufactured the first time. The customer is responsible for the cost.
When you contact corporate headquarters they pass the buck back to the dealer.
I have the 3.8 engine and intend to change the upper manifold before it goes. Also see KenCo.com for a repair to the EGR port so you won't have to change the lower manifold to the new improved design.
Other than that I love my BUICK.