I would try to sand run out with out going threw to base first. by using a small hard wood block starting off with 600 wet holding block at 45* and a very light pressure. stepping to a finer grit as you get closer ending with 2000. If not able to see the sealer buff it. If you go threw it is not much extra to color coat the whole fender, provided you have some paint left. That way you are sure you won't get ring around the repair and end up painting whole thing anyway. Three paint jobs starts building up mill thickness that is not good for longevity. Did you know that reducers that are to fast drying cause more runs than one that you don't really have to try to keep it wet. second most cause is a gun that has trouble spraying a even but wide fan. when you shorten fan from 10 to a 6 your flirting with runs. of course keeping even distance and same angle from panel and even overlaps are important also.