How to fix a loose rear view mirror base? Any ideas??

if it's the type that has a ball and socket (as opposed to a remote-type) you can do like I did to the rear-view mirror in my Duster: to stop it from flopping around, I spread some krazy glue on the ball, then moved it around while it dried (so it wouldn't actually glue it in place). The glue dries and gives a friction surface to hold it where it gets put. Worked for me anyways:D