Assembly process for door mirrors

[Procar Specials]

Best advice is to turn the top part of the side mirror ~ 90° to the window before you remove that complete unit from the door.

Than you have best access to the 2 golden Philips screws, which holds the upper part (see picture)

I have done many of my cf side mirror conversions, sometimes you have to drill out that screws, because they stick like hell into the chassis, even with the 'right' tool.
I replace that damaged screws with Allen screw with lens head (V2A stainless steel)and use some urea grease during installation.
You will never have such a problem again.

There is as can be seen in the photo, a fairly meaty looking spring, so before I attempt the separation, is there a risk I wont be able to put it back together without specialist tools??

No. If the small metal holder at the buttom side is removed, you can carefully pull the glass outside the chassis.
Maybe the white pin will spring out of the chassis mount, but it can be easliy pressed in again.