Had the same on mine a while back,
If it's actual rust there's little point in t-cutting/polishing as it'll just come back.
Mask the area neatly with duck tape or similar heavy tape to avoid removing paint from surrounding area, use medium grit emery paper to take it right back to clean bare metal.
Make sure it's bone dry, use a heat gun/hair dryer to get a bit of warmth into the arch. If the metal is pitted use a dab of Kurust or similar & let it dry, then zinc primer, let it dry, remove tape & touch in with right color of touch up. Job done.