Have a 65ish chevy pickup-bed trailer that I use on occasion. Has the 12 bolt axle under it. Really never thought about checking the diff fluid till a few weeks ago. Bone dry due a pinion seal leaking found that out later talk about a mess. Only holds a quart and half to begin with. Checked all the gears no pitting only a good layer of sludge on the bottom, didn't check the wheel bearings. Been in the family over ten years probably been dry way before then. In use as trailer axle is lube even needed? Replace the seal and buttoned er back up with 80w90 so hoping no more leaks.