set's post in Wing mirror glass replacement 1990 SE was marked as the answer
Mirror arrived quickly and is an exact match. It came with a plastic backing plate and adhesive pads - I didn’t need the backing plate as it was just the glass that had cracked. No heating elements in the glass and no wires in the mirror body, so if it is heated it must be by some element in the mirror body that I couldn’t see?
Anyway; now fixed so I can recommend https://www.ebay.co.uk/itm/372203532748