I own a Lawn-Boy 1991 model M21BMRC (21" self-propelled, BBC, rear bagger). The mower has been great with the exception of the maintenance on the self-propelled system. The issue that I have is not that the system does not work, but that it requires lubrication at the rear height adjusters every use or the unit will not roll backward well. If the unit is used for about 2 hours without re-greasing the height adjuster fittings, the rear wheels will not roll backward, but just slide when pulling the mower back. My Brother-in-law owns an very similar mower (1993 Lawn-boy model 10591) with a completely different self-propelled system that has not had any of the issues I have had with my mower. Now to my series of questions... 1. Has anyone had any similar experiences with an M-series? If so, is there a cost-effective way to modify the self-propelled system? 2. Any good sources of used lawn-boy parts where I might get a drive system from a 1993-1996 model 10590, or 10591? 3. Any other models of mower which I might be able to swap the drive system into my mower? My delimna is that I really like the M-series mower. The bagger on this mower is the easiest to get on/off of any other I have seen, and other than the drive system, I have not had any problems with this mower. I am getting tired of lubing the height adjusters at each use of the mower. Thanks for any suggestions.