Don't know what the recommended schedule is but I rebuilt my 7900 C24's for the first time the other week. It was suprisingly easy. Actually kinda fun. I did not replace the bearings but completely disassembled, cleaned and regreased. They were smooth before but feel even smoother now... at least in my mind Just be careful prying off the front seals. They bend real easy. Being that it was so easy to do, I will probably do it annually.