Yes, fixed it many years ago and it has now lasted longer than the original did.
#1 Unclip gutter trim on drivers side (UK) by pushing back at end while trying to lift about 6" further back.
#2 Peel back and unclip at other end.
#3 Remove slime and debris from gutter. Find tiny crack and test it with a paint brush bristle.
#4 Wonder how on earth so much water can get through such a tiny crack.
#5 Scrape out old filler from panel join in last inch of gutter.
#6 Wonder why they built it with a gap at the end.
#7 Mask area with tape.
#8 Fill with polyurethane sealant like this:
https://www.toolstation.com/shop/p67949 (NOT silicone!)
#9 Smooth over with plastic offcut then cover with touch up paint when set.
#10 Marvel at dry boot, think about replacing rusty jack.
I did not take pictures when I fixed mine so demonstrated on a scrapyard car instead. Although quite a lot of the join is exposed here, I only found the gap at the top corner on both cars.
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TG
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