I cannot see any dry part but that could be my eyes
I do remember that my E36 M3 had heated mirrors that used positive temperature coefficient thermistors, which basically means that the glass heating decreases (due to decreased current) with increasing temperature, and the opposite for decreasing temperature. 43F is not that cold. It might be interesting to see how the mirror heating performs on a really cold day.
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2013 x35i (Space Gray, MSport, CW/CWII, DHP, Premium, Premium Sound, Technology, BMW-Apps)
Retired: '09 C300 4Matic, '09 GTI, '06 750i, '05 C55, '04 R32, '03 M5, '02 GTI, '01 M5, '00 M-Coupe, '00 540i/6, '99 M3 Coupe, '98 M3 Coupe, '96 328i,... '86 4000 CS Quattro... too many to list.