Also mark and put the cables back in same location on the knob part too otherwise when you push the knob the mirror glass may move opposite of the way its supposed to.
That part that goes in the door is pot metal and even just trying to move ene of the crimped over the cable tabs can just crumble off.
I had one wire housing that the crimp was busted off so I put it back in place and wrapped them together with real small wire and now it works great.
My point is that the adjustable mirrors usually only loosen up because one or more of the cable housings came loose from the part that goes in the door.
At the mirror end they are a little tougher. (a little) :D