If you take off the snorkel, open the TB blade and look inside witha small flashlight you should be able to see where the egr tube pokes up. Any goop around it would be an indicator of a leak. The dealer usually puts in some stop-leak tar-like additive which explains the goop.
If you don't know the age of your UIM you should be able to figure it out from the clock like markings on top of it, There will be arrows pointing to the day, month, year it was made and if its original I would definitely plan on doing the whole thing (UIM & LIM gasket) as preventative maintenance.
98 SSEi 111,222 miles.
Intense PCM, LS6 Valve springs, PEMS, FWI. Hawk Street Pads.