I say, take it down and hand pack. The axle makers don't like the EZ system, the public demands it and that is why they do it. IF you fill up the hub with grease with the EZ system, you will put in cold grease....as it heats up going down the road it will expand and blow the rear seal. That will throw grease all over the brakes. Grease will impregnate into the cast iron hubs and you might as well throw them away. You cant clean them....you can wipe them down with thinners, gas, whatever you want, but the grease impregnates into the casting and will come out when it gets hot. The brake assemblys might get saved, but it is labor intensive....You are FAR better to hand pack..
FROM A DEXTER TECHNICIAN: Pack your bearings once a year or every 12,000 miles, and do it by hand.