crangip

I relpaced my interior rear view mirror on my 91 300SL with a used one. What I have noticed with both the original and the replacement is that the mirror housing and bezel are both sticky. The bezel in the original one broke and the back housiing fell off. I know that the deterioration is due to heat and age. My questions are first, is there something that I can do to slow the deterioration on the replacement? I realize that a pertoleum based product will exacerbate or accelorate the problem.
Second, are replacement bezels and back housings available as new or new old parts? The whole assembly even used is costly and I would like to avoid having to spend a lot of money on this item again.
Thank you for any help on this question.
Phil