Double Glazed window panes only (excluding frames) can easily be replaced. I recently replaced three different panes.
I found it difficult to find on a Google search, so I telephoned a spares supplier who told me that they only supplied complete units including frames – I then asked a local caravan repairer and got the same answer, but with extortionate prices. I didn’t want to replace frames because mine are sprayed grey and there would therefore be additional respray costs. I knew they were available because I saw them in a catalogue at the Paris Motorhome Show last year.
I then got a quote from EECO (ideal for obsolete windows) , they were very helpful and cheaper than replacing windows complete with frames.
I persevered ( I had asked on this forum in 2016?, but did not get specific leads to follow then) and I found by trawling down through Seitz Window Spares on the Leisurespares.co.uk website that replacement double glazed window panes could be ordered. I telephoned them and they were very helpful and only required the AGS size numbers – the three windows cost me £690 and there was a 6-8 week delivery time.
No doubt other suppliers can also help – although my original enquiries were not helpful.
By the way – actually replacing the double glazed window pane is very easy……having released the pivot arm stay, just lift the window through 90deg and upwards using two hands because as you get towards vertical, the window just drops out of the ‘v’ retaining groove. I hope this helps others for future reference.