Rings! Been there. I had a very high compression, good running TD that would use a quart every 200mi without smoking. I pulled my hair out trying to find the problem. With 460psi compression and no smoke I "knew for sure" it was not the rings. I replaced the valve guide seals, all gaskets and seals. I finally gave in, pulled the head, pan and pistons. They all looked fine. No severe ring end gap. Bores looked fine and measured ok. WTF? I honed it and put in a new set of rings. 30,000 miles later and I have never had to add any oil.Only thing I can figure is the oil control rings failed but the compression rings were fine. Good compression and good running does not mean the rings are not worn out. Since these engines fun just fine on oil I guess they don't nessisarily smoke when they are burning oil. The first hint is the "CHECK ENGINE OIL" sticker on the fuel cap door. :?