Kaput trannies have been discussed many times here. Benzmac usually suggests swapping for a factory rebuilt, mostly because of the 4 year, 50K mile warranty. The cost is not outrageous if you buy the tranny from them and do the job yourself or have an indy do it. BTW, the warranty covers parts and labor, even if you did not have a dealer do the job the first time. You can also usually get a discount on dealer parts prices by joining the Mercedes Club of America at
MBCA. Even if you don't go the dealer route, the MBCA membership will get you
The Star magazine, which will have ads for parts suppliers.