My 1997 Bonneville had 77,100 miles when I was driving home one evening. The engine was warmed-up and I got on the highway to go home. After a few miles the engine developed a misfire, then 1 mile more the check engine lite came on, I pulled to the side of the road and discover the oil level was low. I put oil in the car and drove home with the check engine lite still on and the engine misfiring. The next day my mechanic discovered the top of the piston was stuck in the #1 cylinder. The rest of the piston discinagrated and put a hole in the oil pan.
I have since put a new motor in my Bonneville but, the reason the engine developed this problem was related to the plastic manifold. Newer model 3800 series 2 motors have a thicker plastic intake manifold. The only problem I had with the car was occassional misfire at acceleration. My mechanic told me he saw evidence of oxygen leakage in the manifold which was responsible for the engine damage.
It may be a good idea to replace your old manifold with a new one if you like your older 3800 series 2 motor.

We are very well aware of those problems. We have a different view of the problem than you do, as we have Gearheads here who have actively pursued better and less expensive options to prevent the problem long-term.

Newer manifolds are not thicker. The newer GM manifolds are the worst solution available. You want a Dorman or APN upper intake manfold with a sleeved EGR passage, and a reduced-diameter stovepipe. And this isn't the end of the problem either.

You also need to get the DEXcool out of that engine and replace your plastic lower intake manifold gaskets with the new aluminum-framed design. DEXcool eats this plastic to bits, as it gets corrosive with age.

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