Disco 2 Tips on fitting wing mirrors?

My latest frustration...
This isn't the first time I've had to replace the mirror glass and I haven't got it right yet.
Yesterday I noticed the drivers side wing mirror was loose and wouldn't adjust. It was only attached on one side. So I took it off and tried to put it on again. I got it on but (not for the first time) had to use so much force that I've cracked it.
My frustration is that I think I know how to do it but I can't do it.
Here's what I do...
There are three parts:

1. the circular part that is in the mirror housing that moves when I adjust the mirror
2. the square/circle fitting thing
3. the mirror itself

I place the square/circle fitting thing on the circular part in the mirror housing.
Then I locate the mirror so that the 'tags' nearest the car are in place. Next I apply broad pressure to the mirror and try to clip the mirror on. It doesn't go neatly into place so I press harder and harder until it goes on. I take my hand away and see I've cracked the chuffing mirror again!
I have tried working from out to in and I've tried pushing it straight on but don't have any better results.

Anyone got any tips?

Dragonwalker said:

Click to expand...

That video's great except that he doesn't actually fit the mirror back in.
Someone more cynical than me might think that that's because every time he tried it, it cracked!

He does say to slide it, not to push straight in.