One note of caution when using MMO for air tools- a small amount is OK, even good for the vane/cylinder however a large amount can displace the grease if your bearings are not sealed (and most aren't in impact wrenches). MMO has an air tool specific
oil that is better for this purpose. The best thing to do to protect your tools is to give it a little shot of
oil when you are done and run it for a secoind or two. This will coat the motor internals and protect it from oxidation until the next use.
I used to work for Ingersoll-Rand Tool division for 18 years.