means original equipment manufacturer the units from racepages.com are good units.The units from autohausaz.com are oe or oem as well.I would be leery of a mechanic that did not know what oem means----it means it was made by the same company that supplied the same part to mercedes the day the car was assembled .Buy a mercedes mass air sensor from the dealer for $450 plus or buy the oem bosch unit for $170 from autohausaz.com you choose
in your case I would choose another mechanic
ohlord
