Do you mean fuel trim malfunction? If you've got codes P0170/173 then yes, the MAF sensor could be the problem. Don't run out and buy a new one just yet, though. The fuel contamination problem may have had something to do with it. If you can, re-set the adaptation data and drive it normally. If the MAF sensor is bad, it won't be long before the CEL is back on.

Regarding the ATF, I checked WIS and found that Shell ATF 3403-M 115, and Shell ATF 3353 are both approved for use by MB. The latter will also work in the 722.9 seven speed transmission.