Finally got the windscreen frame off. I re-tightened 2 of the 3 bracket bolts (left the clamping one loose), nutted the pillar end and hit with a hammer for 10 minuted or so. Eventually it came off. Prior to tightening those 2 bolts, the bracket would just move with the pillar as I tapped it.
I have a new question for when I replace the frame. When I removed the windscreen frame I discovered that along with the gasket there was a flexible sealing compound. Do I need to replace this or is the rubber gasket enough? Any idea what the product is?
Any suggestions would be helpfull.