My upper plenum
2001 Buick Lesabre Custom 3.8
Just checked the date on my upper plenum - 2001. I also noticed the coolant nipples appear to be black plastic, though they look brand new.
With 105K on the vehicle, I can't believe the plenum, gaskets and coolant nipples haven't been replaced at some point. Though my service history shows nothing along these lines the repairs may have been done at an independant shop and not recorded.
Other than a slight oil burning smell coming through the HVAC when the AC is on, I have no symptoms or problems with the engine. Coolant and oil levels are consistently full.
Still, not knowing about the history of my plenum, and the fact that the coolant nipples are plastic, I think it would be a good idea to have all of them replaced. I'm still planing to have all the engine and trans mounts replaced at a good local shop - I'll have them include the plenum stuff with that.