Spindle Nut goes essentially "hand tight." Torque it hard, say 25-ft-lb, turn the hub, make sure it's tight. Then back off and tighten with just your hand on the socket or extension. Since it uses those "smart nuts" you can line the cotter pin up without having to disturb the nut itself again. The "slight wobble" went away with ball bearings. These taper rollers want the slightest pre-load.
Ah Warnt AKiddin when I mentioned those 21mm bolts! Those of us who want a degree of self-sufficiency should pull those, one at a time, clean, and re-install with a "release agent." I used copper NevrSeez, but I think what we're trying to do is keep water out of an exposed joint. Could be grease, gasket sealer, BLUE Loctite.
FYI the REAR caliper mounting is different, at least on E450 pre-2008. Once the Caliper is off, the Rotor would come off. E350 and possibly 2008+ E450 use slide bolts and I (ONLY) suspect a bracket similar to front would interfere.
OK, back to it - I found it awkward to get an adequate breaker bar in place and still be where I could work it. I had the axle on stands, wheels off, but steering straight ahead. Steering to one side then the other might give you a better shot. I don't remember if I ever thought I could get in there with an impact wrench. Access might have been too tight. It's a large bolt with high strength and torque ratings. There's not much risk of breaking one off. Some of the worst-stuck fasteners I've removed I've done manually. Even a good impact just sat there and rattled, but with enough leverage I got them moving. Once those bracket bolts move, spray again and they'll walk out with a "Who, Me?" grin on their little 21mm faces.
