Pull the spark plugs and turn it over. If a cylinder was full of water, it will spew out the plug hole. If this is the case, I imagine you will have to disassemble the engine to determine whether any bearings were mashed or rods bent. It might be cheaper to buy a good, low mileage used engine than to disassemble yours and rebuild it. A new longblock for a Benz must be breathtakingly expensive.