[Ledslinger]

Maybe the knuckle lube does migrate down the axle tube eventually, slowly and reluctantly. So with many services of the knuckle lube, eventully the axle tube gets a substantial amount in it.

My truck was 16 years old when I got it, and there was evidence the pinion had been out because one of the pinion shims was a valve spring shim. So if it went 10 years before the axle needed repair, then it spent 6 years of maybe getting the knuckle lube filled every oil change.

It is difficult to imagine that the knuckle lube may pretty much stay in the ball area. It could be that it mostly gets flung around in there but not out of that cavity.

The service interval for the axle U joints (as well as drive shaft U joints) is 1000 miles. Thats 50 top ups in 50K miles. If it lost a tablespoon down the axle tube in a thousand miles, 50 tablespoons is 25 ounces.

I think it loses some down the tube, and if it is replenished on schedule, a significant quantity can end up in the axle tube. I also think eventually the lube will be at the same level in the axle tube as in the knuckle housing.