[johns cubs]

Hey guys I am having a problem with my cylinder sinking pretty fast while in neutral position but my reservoir always seems to be full. Not sure the problem but am thinking I am going to rebuild the cylinder anyway. Are there special seals I will need to get or are they just ordinary O-rings that would be in an assortment pack? Would like to have all parts on hand before I start the project. Any help pointing me in the right direction would be appreciated!! Thanks in advanced!