the drivers door switch is most likely bad, they get used the most and wear out first, the connector on the back of switch may have come loose and not making good electrical contact, remove switch and check connector and if still not working need new switch, the windows are all on same circuit and either all work or none work so not fuse. extremely rare is a short in wired but not likely.
Clip inside diff comes out after you remove the cross shaft that goes through the spider gears.
You must pull the diff cover off, then remove the center pin and spider gears, then remove the C clip that holds the axle in the carrier assembly.
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Should be same, just don't forget differential bolt and pin removal first to allow you to push axle in to remove "C" clip.
An axle seal leak especially if its a minor leak can be monitored for about a month or so, as long as the gear oil isn't affecting the brake system. If any grease/oil gets on the brake pads the oils can contaminate them and cause the vehicle not to stop properly. A major precaution to insure you can hold off on the repair is to have someone be sure the fluid isn't over full in the rear end housing, over filling will cause the seals to leak, if it is over filled have it drained down slightly with a syphon pump.
Have the axle bearings checked for wear on both sides as well.