Here is a link to the 521 and 541 loader parts manual. https://partscatalog.deere.com/jdrc/navigation/equipment/77758
Click the link and it should open. In the hydraulic section it appears there are 2 choices of lift cylinders. It looks like on some loaders the lift and bucket cylinders are the same and on others they are different cylinders. You don't say which yours is but you will find the JD kit numbers for each in the catalog. Note that multiple kits may be required for a complete reseal of each cylinder.