John's advice was spot on. I used copious amounts of washing up liquid soap all round the glass, inserted glass into rearmost corner then used a metal spatula to lever the glass upwards into the bottom track. I used a small clamp with a block of wood to clamp the corner of the glass at the the top of the B post progressively tightening as I used the metal spatula to lever the glass into position. This corner is the pinch point
First one took about 15 minutes, second less than 5 minutes , I think that loads of suitable lubricant makes the job so much easier