Originally Posted by davidad

shimano for the most part makes the best hubs on the market. If they are not properly maintained and adjusted then problems occur.
If you are going to spend a lot of time in the mud and water then they need maintaince more often. The seals in shimano and all hubs are dust deals and not meant to keep water out.
The newer versions have the oversized aluminum axle are are adjusted with a small amount of preload before installation on the bike. The heavier axle does not compress. The smaller steel axle needs a small amount of play in the bearing adjustment that goes away when the axle is compress when the QR is closed.