These transmissions had a problem with the B2 piston. The original piston will break into pieces. It's easy to check. With the car on a lift remove the B2 piston cover on the right side of the trans...if it's broken there will be a spring and several pieces of aluminum visible. If it's okay, there will be no spring pressure on the cover(since the spring is captive when the assembly is in one piece). When they fail 1st and 2nd gear slip. There is an updated part to replace the original when it fails.
ASE Master Tech
Mercedes Tech 19 Years