...ideally without breaking it!

Would I be better to cut the old seal and replace it with a new one or can I do this and save the old seal?

Only time I have tried to get a (2cv) screen out AND save the rubber the screen broke. If the rubber is old & hard it isn't worth it anyway. Just my 4pennyworth.
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Yes its worth replacing the seal anyway!

Also use a bit of windscreen sealer if your removing screen to remove rot etc?

old blunt screwdrivers, 3m of good strong cord and some lube.

cut old seal and bin it........will be hard and brittle in anycase

So lube, screwdrivers and string. This sounds like a chapter from Fifty Shades. Thanks chaps, I'll order a new seal

Seal it too! Keep the water out

Use a strong cord as you will be really pissed off if it breaks halfway,you should cross the loose ends inside the rubber a few cm to get the last bit of the rubber flange seated...I would buy or borrow a couple of these http://www-img.toolstation.com/images/l ... =274111136 which make handling you screen much easier and your less likely to damage your car removing or fitting the screen. At under £6 each you can't go wrong they are so use full.

I can hook you you with some super strong rope

its not difficult lube is the key

dont just yank the string sort of move it in big circles start centre top and go a few inches one way then go a few the other so that you have the pressure the same as the thing tends to slip off towards the unseated bit some pressure to push it all in to the aperature when the lips over is needed

if it goes wrong take it out and start again dont persist with it if its gone in lopsided

sucker handles are unneccessary its only a tiny bit glass ( fitted a 2m x 0.5m 8mm bit glass the other day;))