Forgot to mention we also try to remember to wash out the spindle taper and the tool holders with methanol to remove coolant residues. This does make a difference because the residue can be very sticky.

You can also get problems with a sticky solenoid valve. If the air does not turn on quickly the eject cylinder moves slowly and does not develop enough impact to knock the tool out. I had this problem on a SuperMini in my home shop that did not have good clean dry air. Pouring methanol down the airline solved that one, followed by rigging up a trap for moisture.