Most "mechanics" that don't know the 3.8 well say that but guranteed 99% it's the crappy plastic GM LIM gaskets gone for a ****!Either LIM or head gaskets. Pray it's LIM.
Neither Fel-Pro or GM. Get aluminum ones like the set I got from WBS. Also replace the coolant elbows while you're at it if you haven't already.
Tapadatass
And it seems most parts guys don't know Dorman makes the elbows.
Both the Fel pro and the GM revised gaskets are aluminum.