Older 500SEL Transmission Needed

I have a 1985 SEL 500 and my daughter drove the car with no Transmission fluid. The Transmission is shot. Does anyone know if I have to get a transmission from that model series (1985 SEL 500) or are there other transmissions that will work just as well.

Also, how difficult is it to switch out transmissions ?
Thanks in Advance

Have you checked with the Mercedes Dealer? You would be suprised how cheap the 722.3 factory rebuilt transmissions sell for. Most of them are around 1500.00 with a 2 year/24k mile warranty. Now these are not "new" products, they are completely rebuilt by MB, but they carry the same warranty as a new unit.(never had any problems out of them either)