SVStu

Is it the black triangular piece of plastic about 150mm long and 100mm wide?

If so, its simple on my 99 so something may not be located properly on yours. Insert luggs at bottom first (near clocks), push top part home and then insert screw and tighten, but not too tight as its not structural, hence the reason it doesnt stop mirror vibes.

Have you got the rubber boot the right way around that the screw fixes to?

I (think from memory) it can be a bugger to re-attach to the screen, used spit and a pair of long nose pliers to pull it through while supporting the frame when I changed screens.

Put some pics up if its a different part.