Spheres are fairly easy to change. You depressurise the system by lowering it to minimum height and then undo the regulator bleed screw half a turn to release the pressure in the accumulator. You will need a strap wrench of some kind and rags to catch the fluid that will leak when you remove the spheres. Sometimes spheres can be undone by hand, which is fine as they don't need to be overly tight. Obviously, you need to jack the back a little and you don't even need to remove the rear guards. The accumulator is a little more of a fiddle as it's not easy to get at without removing the regulator. Someone who knows what to do would have a full set of spheres changed and cleaned up well inside an hour. It's worth having a go yourself. Start with the front.