If you go with the impact wrench to tighten the bolt, try to reduce the torque. Napa just changed a pulley for me and broke the hole out with excessive force. One possibility is to adjust the impact wrench torque off line and check with a torque wrench. The orginal Mercedes pulley was very weak around the bolt hole. The pulley that came with the rebuilt was very substantial although a little smaller than the original. Still worked ok within the range of the belt, spring and shock. This on a 87 300dt.