Thanks for all the help - I'm going to go to a marine supplier up the road from me at lunch and try and get some "Captain Tolleys Creeping Crack Cure" as it looks good.
I'm also going to get some clear silicone and put this on too.
Just glad I don't have to take the windows out yet!
I'll let you know how I get on - if it stops raining eneugh at the weekend to do it!
Stuart