Since you are concerned and want to keep your car from having any future issues. The best fixes remove the potential of the issue.
Plug the lower intake manifold coolant ports that feed into the UIM/throttle body with 1/4" NPT plugs. By blocking off the coolant, you remove the possibility of it getting into the intake air delivery area. The ports are there for minimal reason and there is no loss or issue from blocking them.
Change the LIM gaskets to the GM aluminum ones and you are all done. No need to replace your UIM, you blocked the potential issue by blocking the ports.
00 Regal GS: All kinds of cool stuff.