My 98 Bonneville SE is N/A (no upgrades what-so-ever). It currently has 152,000 kms on it. I have heard that there are a rare few cars that do not have the UIM or LIM problems. I am actually going to get the car on Monday, but I want to be cautionary to keep the car in best shape as possible.
When thoroughly inspecting the car, driving it, and letting it idle, I noticed nothing wrong with the oil, coolant levels, or anything at all for that matter. Would it be wise to get the UIM gasket replaced as soon as possible if it has not been done already? As well, I have read that it is not too much extra work to get the LIM gasket replaced as well, but it is also extra money. Should I get the UIM gasket replaced, and if so, should I also get the LIM gasket replaced, regardless of the extra moola?
Thanks!

My recommendation would be to do the LIM gaskets also. You're 90% of the way there when you pull the upper. It'* pretty much a given that the lower will go, so why tear it apart a second time? Once you pull the lower off and take a look at the gasket, you'll be happy that you decided to replace it.

Edit - Be certain to get the aluminum framed LIM gasket.