Regarding the rebuild kit for the Shimano M-520 - I don't think Shimano makes one. But that pedal uses loose 3/32 ball bearings and you can replace all of them for about $2. You do need to invest in the Shimano Tl-Pd40 pedal tool to get them apart - it costs between $1.50-$2.00. And this is one of the main reasons I like Shimano SPDs... they last a long time and rebuilds are simple and cheap.