HELLO. From personal experience I would would change out the ALUMINIUM STUD that J-CAT refered to with a BRASS version. The aluminium stud heats up so much with all of the amps going thru it that the plastic holder melts then the nut loosens up causing even higher resistance, more heat until finally a very bad connection. The brass version will take the AMPS in stride. My mothers CAPRICE had this problem & the BRASS replacement did the trick. I would try this simple fix first then the new alternator etc. I bet the alt. has probably been replaced during the last 16+ years any way.
HOPE THIS HELPS