My rear view mirror is fine, but I just bought a dash cam that attaches onto the mirror. The extra weight makes my mirror droop every few minutes, so I had to take the dash cam off.

How can I make my mirror less moveable? I don't want to glue it in place, but want to make it a lot harder to move. I don't see any way to tighten the mirror, it's just ball and socket; I don't even think they lube it. The ball simply rides on the plastic rim.

I'm thinking what I need is the opposite of a lubricant, something that increases friction, sort of a glue that won't dry.

Any suggestions?
1991 300d, 208k