Trim is held on by slots over a mushroom pin on the roof at each end & friction along the channel, the front pin locates in a keyhole slot.
At the front by the windscreen, push trim backwards while lifting it about 6 inches further back, this will disconnect the pin from the keyhole, then just peel back and you can disengage it from the pin at the rear end. Easier done than described.
Duff sealant fills a 1/4" hole right at the back, surprising how much water can pass through a minute crack.
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TG