Dirt bike burning transmission oil, why?

sounds like the crank seal is leaking if the ring was going out it would be down on compression if the ring was just plain gone it would really be low on compression and when you pulled the spark plug it would have metal shavings on it or look charcoal gray by that time you would have to get a new cylinder or bore it ,another way to tell is it would be making a knocking sound from the ring being burn out or it is other wise called piston slap