I know this is a very old thread, but I'm posting this information in the hopes that it may help someone out in the future.
The roller at the rear of the FC200 mower rides on two roller bearing hub assemblies (6687612). They are fairly similar to a trailer hub. If you have some basic tools, they can be disassembled and the bearings can be replaced... Bobcat only sells the complete hub assembly, for around $700. New bearings are about $70.
The bearings are widely available 32205 and 32207 wheel bearings, and the seal is a 58x72x8 wheel bearing seal.
Hope this is helpful for someone down the road.