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The guys at the shop told my missus you need special glue but I think they may have misunderstood that it's just for some trim and not the windscreen itself, as they were talking about pressure testing or something. This trim has already been glued and held for 3yr (previous owner). I was thinking Gorilla Grip but I think it expands too much. Silastic was another option but I don't know if you can get it here and I don't know if it's strong enough.
The last time I checked the stuff used by autowindscreen-type places/vans was pretty special and not routinely available to the public.
Building/Construction silicone does not work, (no not my attempt, but the 'work' of the geezer I bought my Grand Espace from).