The "whole assembly" is in two big parts, I forget their names, but the bearings are in them already greased. So you start over, no worries about past bad maintenance.
You still need to do the electrical side. Mine pulls 12 amps (3 per wheel) which I see on the Trimetric when the breakaway switch is yanked (only do that with the 7-pin disconnected from the truck!)
The garage also checks the equalizers and shackles etc while down there, so you should too if doing it yourself. The bushings for the bolts can wear through and then the bolts wear bigger holes till it all comes apart. Nasty.
You just keep throwing money to the garage guy for his holiday in Hawaii while you shorten in your RVing holiday plans :(