I would think a 10 psi difference is from inconsistant test procedures. If the rings are worn, oiling the cylinder would bring compression up close to other cylinder readings(temporarily of course). After oiling the cylinder your compression stayed relatively the same which would seem to me to be the beginnings of a burned valve. You better do a leakdown test or have qualified person do one to try to pinpoint where the compression is going. You may get away with a cylinder head pull rather that the lower end.