It's not unusual for these automatic Mercedes trannys to requre some 'shift by accelerator' input from the driver. If the 'late-shifting' is something you can deal with and it's not leaking significantly, just keep an eye on the fluid level. Tranny filler & dipstick is underhood at right rear of engine. Check with engine warmed up, parked on level surface and idling in P. There's also a cold fluid level mark, below the warm fluid mark on the tranny dipstick - see your owner's manual.

Happy Motoring, Mark

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DrDKW