Locate a spare transmission for it and get it rebuilt ahead of time. The 300D Turbo trans likes to go out around 150-200K.
My mechanic is a Hispanic gentleman in Dallas who is a former Mercedes Master Mechanic. Somehow, he is able to source parts for me way under what a dealership charges and his labor costs are dimes on the dollar. I buy minor parts at O’Reilly, believe it or not.