make sure all the old gasket is out. clean with a razor blade.
all i've ever done to glue them n place is to put some stiff axle grease ont hem and press the gasket into it. don't worry about using too much. extra greease will either extrude to outside of cap to be wiped off.. or to insid ewhere it will disolve in the oil.
i use this to tack gaskets in place too.
i'm not a big fan of rtv. it does have a few uses though.