Is it the bearing? or is the wheel on the bearing? If it's the wheel that is toast, you will have to replace the entire trolley mechanism (that is all that HP sells). It was $1600 last time I checked.
If the wheels are getting chewed up, have you been keeping the bearing rails clean? Are there any nicks or marks on them? It should be part of your daily routine to wipe these down so they are free of dust, debris, or any buildup. The bearings should also be cleaned. I don't remember what the book says to clean them with, but while the printer is in sleep mode you can freely move the carriage back and forth holding a q-tip moistened with alcohol or whatever the book says to wipe the bearing wheels.
If it's the bearing, a machine shop can replace it for you. It's a common bearing, but the wheels are specially machined with a lip and I couldn't get anyone to make it for me. Someone may have a spare laying around.