It's one of the main part of the transmission, controls the direction and pressure of the ATF.
Valve Body part# 140 270 06 06 MSRP: $1070.00
Also necessary: original MB ATF, filter, pan gasket and about 4 hrs of labor.
It's not something for a backyard mechanic to do. If there is a problem with the valve body, I'd strongly suggest to take it to a MB specialty shop or to the dealership.