I had the unfortunate experience of having my transmission break down.
I checked with the dealers and they were asking something like $2000 for a rebuilt transmission (they didn't carry new ones). But I opted to get mine rebuilt for several reasons. MB requires a deposit and if they determine that your core is no good, kiss your deposit good bye (I can't remember how much it was, but it was a lot. Do a search and read my post). The other reason I had mine rebuilt is because the mechanic I go to uses only OEM parts.
By the way, my car is a 86 300E