I realize this is not exactly a Spec Miata question, but this should be the place with the knowledge.
My son's 99 Miata is drinking oil at the rate of about 1 qt per 300 miles. The PCV has been replaced. Cold compression is 210psi in all cylinders. Can't see any blue smoke, although we need to investigate that more closely during transient conditions. There are no external leaks. It does have the "EGR" engine code, but that does not seem like it would be related to oil consumption, since it is pushing exhaust back into the intake (the oil consumption might have caused the EGR code though).
My question is whether or not it is in the realm of possibility for this much leakage from bad valve stem seals? If not any other suggestions?
Thanks for any thoughts you might have.