Maybe take the glass out (decent windows fit from the inside) which
should make the operation a lot easier.

D'oh - I hadn't thought of that

We had the sealed units replaced a few years ago (cos the wife likes leaded
glass) and it was all done from the inside. One flap has opening windows
each side, so that should be reasonable anyway, but taking the glass out
will take a lot of weight off. The other one, we can remove the glass in
the non-opening pane beneath the flap and reach up.

Thanks for that - I feel a lot happier now

Al.