Power relay points will always have pitting and ablation, especially on DC circuits. There's NOTHING you can do to prevent it, it's just part of the inrush amperage when closing in on a load. If the relay is working, leave it alone. Trying to be a hero and abrading the points will quickly remove the plating and rapidly cause the relay to fail. This is not a set of breaker points. The plating on the relay points is very thin, sanding them will take the coating off.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)