Thanks everyone, as ever you have the answers.
Job done but certainly not the easiest especially as you have to impart no little force on the glass edge. Benton's U Tube link is very useful but made it look easier than I found it and doesn't cover the complication of heater wiring. What I learnt: 1, Ensure you have the glass the right way round in the frame if the glass is heated - blue wire to the left. Also on my glass you can read the etching from the outside. 2, Fit the seal to the glass first! 3, Only lube the seal to the frame, don't allow lube to get between the glass and seal. I used Silicone Lube. Next time I will spay it into a pot and paint it on. Goes everywhere with a Aerosol. 4, Take care to get the heater wires into the grooves in the corner blocks. Not my favourite job! O.G.