There are several grease fittings on the hydro linkage. Some of them are hard to find. Are you sure you are greasing all of them? If you have a belly mount mower, I would suggest removing the mower and lay down under the tractor to find all the grease fittings. If you have an operators manual it should point them out. Sometimes it is necassary to disassemble and clean the linkage to get grease to flow into the joint where it belongs.