on black moulded semi-glossy parts such as this....which are incredibly plentiful on modern bikes....the best i've found that one can hope for in a "home repair" is smoothness and masking of the scuffed area. what i've done many times is gently wet-sand the blemished area with 1200 grit paper or a # very close to that, inspect for smoothness then continue to very lightly sand until satisfied. then i use PJ-1 satin black cyle engine case paint after wiping down sanded area with suitable pre-paint cleaner such as prep-sol. the trick is to be gentle, have area squeaky clean and wax/grease free....then lightly fog the area with PJ-1 a few times till satisfied. after the paint has cured at least 24 hours you can then put a small amount of protect-all or similar vinyl shine treatment on a clean rag and wipe down the entire bag to blend it all in. the job is tedious and a bit time-consuming but a hell of alot cheaper than the alternative of component replacement.