So, while tearing down my bike recently for a pre-season inspection, I was surprised to discover that one the rear wheel bearings had completely seized despite there being no obvious signs of damage to the bearing itself, although the end cap showed some suspicious, uneven scoring past the seal.
The OEM rear hub uses one 6005 bearing on the drive side and a smaller bearing on the brake side. Here's the bearing replacement kit for the OEM hub. The loose bearing lying on top is also a 6005.
And here's the drive side:
Removing the SM Pro bearings is relatively straightforward using a drift to knock aside the inner spacer tube and then tap out first one side, then the other, by driving on the inner races.
Rather than buy Moose or All-Balls replacements, for about the same price (or less) I picked up some better quality SKF bearings and seals from a local distributor. The 6005-2RS is a common part used in many industrial and recreational applications, so you can get them pretty much anywhere--including where sleds and ATVs are sold.
Installing new bearings was equally straightforward once I found a 34mm socket to use as a driver. I would've made a tool, but didn't have any rod stock in the required diameter. Sometimes buying a socket is good enough.
With new end-caps installed, the wheels feel buttery smooth again. Here are the old ones showing part numbers:
The lesson here is to not assume that even relatively new bearings are still good, and to check them all carefully before heading out on your next adventure.