Golf Cabriolet 1990 rear view mirror

Can anyone recommend a replacement mirror for the Golf Cabriolet? The existing one is attached to the windscreen with a base plate but has been bodged over the years and has finally given up the ghost. The existing base plate is welded to the windscreen - any idea how I can get it off with damaging the screen? It looks like someone has tried to glue the mirror to the bracket at some point so it's not in great shape so needs removing. We've been using a stick on one from Amazon but it didn't last long.

The mirrors on this side of the pond are attached to the windscreen with 2 part glues, that with a good sharp razor blade can be scratched off.  I would mark the Button position on the outside of the windscreen with a sharpie.

New mounting buttons are fairly cheap less than 5 bucks USD, and over the years I have found that Clear Silicone RTV works best.  Place a good dab on the mounting side and press firmly to the Windscreen, then cover with blue painters tape to hold it in position for 24 hrs.  When it has set, you pull the tape off and then with a razor scrape any over spill off the screen.  

I found that the Clear silicone while not instant as the specific button glues, tends to work better and hold longer.

There should be a little grub screw which holds the mirror in place onto the metal fixing on the windscreen  find another grub screw to fit the mirror then you don't have to try and glue it on.