I checked the production date on my Delphi upper intake manifold and my cars production date. Both are December 1998. So I guess the theory of the revised UIM and LIM being used in late production Bonnevilles is not right either. My car is a very early 99 and has the revised Delphi UIM and the revised LIM with smaller diameter EGR tube. The upper intake was not a problem. The LIM gaskets are the ones that failed.

Regardless it is obvious the Delphi manifold is the original one that came on my car. The LIM is hard to say if it is original or replacement at some point between 0 and 80,0000 miles. I really think it is the original however.

So have we actually had any 1999 Bonneville owners with a UIM that was damaged from the EGR tube? If not then it is probably safe to say that 95-98 Bonneville owners with the Rochester are the ones who need to worry about the UIM failures. The 99 to newer owners with a Delphi are probably safe.

Harry (57chevythunder) had his UIM fail.

I think you're assumptions are right. It'* just the lowers that we ALL need to be on the lookout for.

Yes lets start a discussion about the lowers. We already beat this one to death.
At least I now know I have to look for a used revised intake pipe.
Don't really want to take it back apart though........

My car was manufactured in July, 1999. The only problem I've had with it is a leaky throttle body gasket in 106K miles. I was considering, for a while, doing a preventitive replacement of the upper and doing the LIM gaskets at the same time, but based on some stuff I've read here about '99 cars, I may just wait.

I do watch the coolant like a hawk.

I wonder if my car has the new, improved EGR pipe, and if so, if they also made some improvements on the LIM gaskets at the same time.