Any Mercedes properly taken care of gas or diesel will run 300k-400k miles.
250k is about all you can expect out of a tranny, anything more is luck, some people are very lucky.
I wouldn't buy a car with more then 300k miles on it, they start to need everything and have a lot of slop in everything. 400k is really starting to push it, engine wise. A 400k mile engine is a crap shoot.
This is assuming you drive enough to put the miles on in a reasonable time, before age starts killing stuff.