Yes, replace both. There is not enough material on MB rotors to turn them and reuse the old ones. And the OEM parts are cheap enough, so it should not be such a problem. I think the front disks were $50 - $60 (USD), on my 1989 W126 car, and the pads were average price too.

Good luck!

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1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)