These are easy to take apart with a 10mm socket.  Clean and lubricate with White Lithium and Teflon grease.  Adjust tension to be snug for pivots.  They should move with some force, but not move easily.  Mirrors were replaced with 914Rubber.com additions.  The plastic backing that is clear and cracked it to keep the water off of the back of the mirror to prevent pitting.  Aftermarket ones are available (sometimes).  The older mirrors from the 72' seemed to use these backings.  Those pre-73 mirrors have a different shape and mirror.