About a year ago I had to replace the seals behind the front wheel hubs that keep dirt out of the axle. I had spent too much time spinning the wheels in deep mud, trying to get unstuck. Shorly after, the seals started leaking.
Anyway, when the hub is removed, I can get a look at a portion of the spindle mechanism. What I noticed (when replacing the seals) was there were some metal shavings settled in a low spot in the left wheel side, but not on the right. I wasn't too concerned, because everything had been working properly and I figured they were just left behind after some milling procedure when the axle was made.
In retrospect, I wonder if the bearing had already failed and was turning up cast iron shavings? I will pull the right wheel hub and look for shavings. Even though the lubricating oil is free to move anywhere in the axle, some of the axle sections seem reasonably isolated from adjoining sections. If there are metal shavings behind the right hub, I don't think they will have migrated from the left side. If all looks good, I may not tear apart the spindle to get a first hand look at the bearing.