What'* the date stamp on the the top of the UIM? These things have a date stamp with an arrow pointing to the year. If its anywhere below 2003, you need to replace it.
The problem with these is that you have a very high chance of it just completely letting go one day and hydrolocking your engine. Hydrolocking your engine while in gear going 70mph on the highway isn't a good thing. Its very easy to replace. Dorman makes a revised kit with a revised stovepipe which I have installed in the past. You can replace it a dozen times but if you don't fix the cause of the problem, you won't get anywhere.
Get the Dorman kit, which has all of the gaskets and o-rings you need, and as Bill mentioned, get the aluminum LIM gaskets.
2005 Pontiac Bonneville GXP - For Sale ----- 1995 Buick Regal GS(X) - L67 madness
2000 Buick Regal GSE - Stock...for now
----- 1987 Jaguar XJ-* V12 - 12>8