All the the newer MB engines have "knock" sensors that detect spark knock. IF the check engine lamp comes on for MAXIMUN retard on any cylinder then the engine requires higher octane fuel.
The engine has 10/1 compression & should have at least 90 octane for CORRECT performance.
Long term damage can be done by using low octane fuel.
However if the engine is never accelerated briskly I doubt if any damage would be done.
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