Brush painting works great also. As you know first you must have a very good brush to lay the paint on evenly and with out or with minimal brush marks. The paint will flow well enough to give you a nice smooth finish. You gotta have a slower drying paint so it flows and fills in the brush marks. I have also used brushes to touch up Harley Davidson frames where they get some abuse from road junk, and also where the older models would dump battery acid onto the frame from the overflow tube that was not installed properly. Sure it works very well.I still believe in spray painting my engine components. Some times you would do this to match the outside paint, the body paint.