Well the one on the right looks like a used mirror and the one on the left is new right?

The sticker heating element is sticky on the backside, I think that's just the backing of the glass that keeps it affixed to the backing plate, I remember mine was like that too when I replaced mine.

The right side one just has some age to it and probably why you were seeing degraded performance. I just put dielectric grease on my electrical connections and hope to get another 9 years out of them, just like the stock ones.

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards