i just got my bass back from my grnadads, it was left during my move to kalamazoo. and it hasnt been played for about 4 months. when i took it out of it's case, i noticed some of the frets looked rusty right on the edgr of the fretboard. is there a way that they could just be dirty, and if it happens to be rust. is there a way i can clean my frets so that there isnt anymore rust.