Could you use sanding sticks to sand it back?
https://www.scalemodelshop.co.uk/15pk-mini-sanding-sticks-albion-alloys-360-p14749/
Attach one end to a drill and spin it to speed things up
or a flexible file
https://www.riogrande.com/product/ultra-thin-micro-flex-files/114038GP/?code=114038
this could very much work. i gave this a go when i had trouble pushing an hydro hose into a tight downtube guide ( the guide goes all the way ). there was some metal residue at the bends, luckily next to the entry point.
@fredtc started
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Could you use sanding sticks to sand it back?
https://www.scalemodelshop.co.uk/15pk-mini-sanding-sticks-albion-alloys-360-p14749/
Attach one end to a drill and spin it to speed things up
or a flexible file
https://www.riogrande.com/product/ultra-thin-micro-flex-files/114038GP/?code=114038