Duracoat isn't super cheap, but it does work remarkably well, and is extremely tough. Turned a pretty beat-up eBay find from scuffed up sadness to nice and new. This is HK416 Black, which is a virtually flat black (tiniest bit of sheen.) Duracoat makes about 30 different blacks, from full gloss to full matte, so I'm sure you could find one to suit you. You can
get it in a rattle can for about $35 and one can would paint an entire frame-- so if you have any other parts you want to match/refresh, this is the ticket. Works on pretty much every surface, from carbon to metals to plastics. I use the bottled + hardener through a small gravity-feed HVLP ***, but I've used the spray can in the past and the results are identical.
Before:
After:
