Good job. I too have an NAA. Rebuilt my old pump a few years back and had the top cover off 4 times. Each time there is dirt in the sump. I wipe it out, spotless, but the dirt seems to get into sump via the lift arms and the top link.
Could you install an oil filter on your suction line? My backhoe has an oil filter on the suction side. If I ever need another pump, you'll be hearing from me.