thanks for your reply
I spoke to Ocean chandlery who supplied the replacement acrylics and they suggested heat ,maybe boiling water on the ali frame where the join is
apparently some frames part easily ,some do not.they thought bavaria when originally fitting the hatches put anti corrosive grease on the joins and if they put too much on then this makes the joins harder to separate much later on
I used a combination of drilling out or carefully cutting a new slot in the screws ; the screws in the hatches were much more corroded than the port lights
I may end up buying a new hatch with frame and sending back the acrylics and seals
Ocean have been very helpful