just did one at work about a month ago; big chunks of metal in the pan.
got a reman from the dealer; list price was something like $4000 which included a new torque converter.
wouldn't gamble with a rebuilt from an independent rebuilder.
i agree, most newer MBZs are cr*p. get a Lexus...
the last of the good ones was the W126 IMO.
if you want to vent, here's a site dedicated to peoples' MBZ ownership woes. you are not alone.
http://www.mercedes-benz-usa.com/index.php