Dremel with a cup brush makes fast work of ground contact points. Then, lather the bare metal with dielectric grease. Place a stainless steel star washer between the grounding lug and the body/frame. I'm currently refreshing all the grounds of my 1993 Chevy C1500. The vehicle is currently experiencing a intermittent engine drop-out once heat soaked. Although I'm pretty sure the issue is not a ground one, refreshing the grounds on this old of a vehicle is a wise move in avoiding future age-related electrical issues.