It is DIY 'do-able' with patience. See my comments to Pete above and my earlier contributions including.
"I would guess your frames are similar & same original supplier as those on my 8m. Check-out http://www.sealsdirect.co.uk/ . I ordered online, FWR148 for the channels and OWS783 for the sliding seal. They are not cheap but the perfect replacement. One word of warning, once out of the superstructure the window frames have to be split at the mitres which, for us, was a pig 'cos they were secured by rusted mild steel screws."