How do you repair leaking stabilizer cylinder on john deere 410b backhoe?

Depends on what is wrong. First step is to disassemble the cylinder..if the leak is small (seepage) then you can typically rebuild it with kits availible online for less than 100 bucks and a few hours. If a kit you order does not come with instructions, you can usually find disassembly/install instructions on the web. Unless the shaft is bent or excessively pitted, this is the cheapest and easiest way to repair it.