compression test wont really diagnose worn oil control rings because they dont really add to compression as such, you really need to do a cylinder leakage test to comfirm it is the oil rings, when you say you changed the head seal do you mean the head gasket? and if so when the head was off did no. 1 piston look damp or a different colour? and does it foul no. 1 plug when the engine has been on overun for a while? for instance going down a long hill with no throttle!