If bearings wear out as quickly as DOS states there is an evident design problem. I don't have any knowledge of current Shimano hubs. The longevity champ remains Maxicar hubs with shielded annular bearings. Most who ever serviced those did so only to see what was inside that lasted so darn long. 100,000 miles was normal. Spoke holes lasted that long too. They were heavy. Sanshin Gyromasters and most of the proprietary versions of that hub gave very good life with simple bearing replacement. I am now riding a 1960 version of Sanshin, no idea how many original miles, I've done 5000 and the bearings remain very smooth. Maxicar and Sanshin were freewheel hubs, both had axles with a reinforced section that ended the possibility of axle breakage. These are very old engineering issues. Expensive modern hubs should work.