I have not done a tranny swap as of yet and am sure someone will chime in, but from the looks of the transmission itself and the access you have to it in on your car, I don't think it will be very difficult. For the most part these cars are pretty straightforward and easy to work on.

Congrats on the car and welcome! I wish I were closer, I am great at drinking beer and telling people what I think they should do.

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1981 300TD
2005 C55
2004 E500
1999 ML430
1992 400E
1998 C43
2001 SL500
1988 300SEL
1986 190E 16V
1991 190E 2.6