Glass missing from friend's 90 240DL driver side mirror. Manual mirror (and I assume not heated unless heater switch is also rear window defroster switch) no separate mirror heater switch is present.

Looked at this site, turbobricks and googled but do not see situation similar to what is on his car.

There is a semi-firm rubber membrane that is the size of the mirror glass and that moves with the inside lever. We have the correct size mirror glass but I am unsure if we are supposed to adhere the glass to this rubber membrane or not. All of the pictures that I have seen show a hard plastic facing (some with a white ring) that the mirror is supposed to be glued to.

Any help with these questions would be appreciated

Did 90 240's have manual heated mirrors?

If so did the rear window defroster switch control the mirror element?

Is the heater element in that rubber membrane? It feels like it might contain wires.

If the rubber membrane is the heater element is special mirror glass required?

Thanks
Howard