I live near the beach and we get a lot of sand round here. It' probably occurred on window operation by a build up of grit on the internal roller, scratching the surface.
I put rubber gel on the glass over the scratch run and then took the windows up and down a few times. There was no sound suggesting the roller was off track etc and the mark had not increased. However it's not really possible to tell without taking the door card off I would think?
As a remedy I applied some fine body scratch repair paste to the mark, (small and vertical around 7cms in length), with partial success. However conscious of 'novice damage', and leaving a 'bloom' on the surface, I went no further.
On the net tonight it seems best to try a resin/filler first, before elevating action to a harsher level? Has anyone tried these and if so what were your results please?
Resin
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Drill assisted Kit
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