Repair to plastic mirror mount

[Memnon]

On my new car, I clipped the mirror (arrrgh)pushing it fwd instead of its intended folding backwards.
Garage disassembled and put it all back to working ... at no cost.

However the mirror mount has a square peg, which motorised mirror opens to, and it had been forced part that .... so the corner of moulding is scratched/scuffed
Anybody aware of a neat gloss black filler I can apply to fill in this cosmetic damage