Interior Mirror Screw Cover - How to remove ?
 

I'm trying to fix my blurred rear view al la SIDC common problem sheet - http://www.sidc.co.uk/faq.htm#3.4

I'm however struggling to remove the screw cover.

I've tried a small screwdriver, but stopped short of damaging the plastic, and I've pulled it this way & that (oh err misses) - all to no avail.

Is there a "secret" technique ?