I have never understood the idea behind using a vehicle differential for a trailer axle. Not that there is anything majorly wrong with it and to each his own and all that rot, but I figure if a differential is cheap enough to get from a junk yard it probably is indeed junk.
Changing oil in your trailer axle sounds wrong.
A really good trailer axle is cheap. Probably cheaper than a junk yard differential.
Most guys that build trailers can weld, make your own axle and really save.
On a positive point, if the differential is in reasonable condition you can mount an alternator to the pinion gear and have a great power source. I have never seen this done, but I have been tempted.
2006 Solar Yellow Rubicon Unlimited
Jeep Club Member #1340
6 Speed, Hardtop
Mods done: Hurst tee handle, cheap hand throttle, Rokmen Merc front bumper, Warn 9.5 TI winch with 3/8" X 100 worth of Viking yellow rope, DPG OME Ultimate with JKS ACOS up front, Kilby Gas Tank Skid, Kilby Steering Box Skid, Jeep Medic Belly Up, Skidrow Engine Skid, Rockcrusher Diff Skid in the rear, Warn Diff cover in front, , AR Outlaw II's and MTR 12:50/15's, Homemade rear Bumper, Cheap Cobra CB, Puma OBA, Sirius Radio, Locker Defeat, Rockhard cage, Rockmen short corners, homemade tire swing/tailgate hinge affair, Airlift air bags on the rear- - - - - - and more to come!