After having seen a pro do it I'd have no hesitation in trying it myself in future, windscreen excluded. Starting in the middle of the seals top run, inside, just prise the rubber over the lip to around 3/4 of the way down each side and the glass pops out. The fitter recommended/uses Arbomast but Wickes sell a Unbond butyl based gutter sealer that looks very similar if not exactly the same. The guy also said on NO account use silicone RTV type sealer. Will probably use the Unibond stuff if I can't get any Arbomast locally tomorrow. Pretty certain mine was the original glass so they must've used sealer on the production line.