the 3.8 head gaskets usually dont leak to the outside of the engine.
keep tabs on your coolant level, condition (see if it has any oil in it), and your oil level and condition. if either do anything strange, there is a possiblity of a bad head gasket.
they usually fail between the water jacket and cylinder (the end cylinders are most common). sometimes you can see air in the coolant (or a geyser out the rad cap if you remove it and start engine). those are definate bad gaskets.
the biggest thing to keep the head gaskets in good shape is frequent and regular coolant changes. and make SURE there is no air in the system to prevent hot spots in the heads.