Yeap, I knew they run nitrogen through them just for the reason you stated. I used to watch Howard Hurd at his house using a micrometer on his impact wrenches after his modifications. He did a little extra machining to them so they could spin faster to handle 200 PSI. He may have added ball bearings to the shaft, I can't remember. It got to where he was building so many of them, he had to outsource some of the machine work, but he would take each one apart to check it out. His grandson, Jim Hurd, moved the basement shop to a commercial business in Hampton, Ga. located right before you get to Atlanta Motor Speedway. I have always put oil in my impact drivers too. Sometimes I ran an inline oiler below the handle, or will take out the little hex plug in the tool body and fill it.
Guess I spend to much time in the garage. 
