I have a YZ400 98 model bush basher, it does what I need it to do in general but the rear shock leaked all its oil out and now has no dampening effect so it bounces around a lot over the bumpy terrain. In the manual I have, it says these shocks are only able to be replaced, not serviced. Is this true does anyone know? Has anyone ever done the rear shock seals/valving themselves? I have a friend who has access to nitrogen tanks, so that part of it should be alright.