You are fine with 87 octane. MB didn't start sepcifying high octane until I think 1986 .If she pings, go up to 89. Still pings, then put in the "high test" gas.
BTW my 911 calls for 87 as well. I can certainly run it on higher octane, but it will run without issues on 87.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member