While you have it apart it's a good time to look at the wheel studs, checking for excessive corrosion or flattened threads. Better now than when you torque a nut on and have the stud snap! Also, I'd visually inspect the gears for chipping/cracking, signs of this could also show up in the oil. If it's primarily a plow truck, consider a synthetic oil, it will not be as thick in cold weather. It usually costs more but sometimes it goes on sale for the same price as dino oil here.
Also, thoroughly clean the brakes with brake cleaner and look at the hardware for any springs or clips that may be on thier last legs. Hardware kits are cheap, I usually replace mine when I do the shoes regardless of their condition for safe measure.
As a side note, I usually stamp the month and year that I last serviced an axle to make keeping track easy, just as you would on a compressed air cylinder.
1
