Rear quarter light (Side window) chrome trim finisher

Just been to have a check on our Elf to investigate why the wipers packed up during a freak storm yesterday, and spotted RUST! The chrome trim around the opening rear side window doesn't reach all the way around the glass leaving a 5mm gap between it'stwo ends at the bottom. The previous owner has obviously tried to fill this gap with silicone and stuck a finishing piece over it. This piece has rusted away, subsequently trapping water between the window and the rear wing, which has now started to bubble. I'll sort the rust quick but I now need to fill the 5mm gap. I've had a look on Somerford Mini and there doesn't appear to be such a trim finisher. Can anyone point me in the right direction?

some (earlier?) 1/4 light windows had 2 gaps (top and bottom) but the best ones to have are the ones with just the one gap so best bet would be to find a good used replacement....

Should there be a physical gap of 5mm though Al? I saw on Somerford that there were two types but they look as though they but up pretty tight closing the gap I currently have.

Can you put a photo up Si? I'm confused at your description.