power gear levelers seal kit for rebuild ?

Those listed as non-rebuildable are most likely welded on both ends - no real way to take it apart and rebuild it. In those cases a good shop can machine open the one end, do the rebuild, then weld it back together. On a cylinder the size of a leveler it shouldn't take all that long either. Our shop often reworks/rewelds cylinders. You just need to find a shop with capable people.