Mercedes specifies premium fuel for M103 engines, but with only a 9.2:1 compression ratio, many will run on lower octane than typical pump premium. It comes down to individual cases and there are a lot of variables - ambient temperature range and altitude, individual driving habits, and internal carbon buildup.

The only difference between regular and premium grades is octane rating - nothing else of any consequence, so select the minimum octane fuel that will allow your engine to operate without significant detonation. Occasional transient detonatation will do no harm, but sustained detonation under any driving conditions can be harmful. Detonation rapidly overheats combustion chamber boundary surfaces and can lead to piston and valve failures.

The Bosch KE system automatically compensates for variation in air density, fuel specific gravity, and fuel oxygen content (if any) to maintain the proper air fuel ratio for all driving conditions.

Duke