On the quarterlight glass, not the frame..
so they went in from the drop glass side.
People can be strange about external car mirrors. Down here in Oz, many years ago the powers that be decided (on unknown evidence) that wing mirrors were bad, and all externals should be on the front doors. This caught many Japanese imports out, and we still see fittings on the wings that were intended for mirrors, but have been plugged - easier and cheaper than removing the whole fitting.
I probably ought to just bite the bullet and put some Winguards on the doors
No, don't do it!
No, don't do it!
I like my Winguard door mirrors, they suit the car and give me an excellent rear view of the road.