Depending on your vintage, your Liberty Aux Pump has a small filter that should be changed periodically. Mine is tough to get at, just in front of the front axle behind a steel access door only accessed from underneath. Properly jacked and supported of course.
IMG_3417_1..JPG
Round black cover just rotates to loosen
IMG_3420_1..JPG
Filter with cover removed
IMG_3423_1..JPG
Filter