Pinpointing cause of oil consumption-lower end or valve guides?
Sorry, this is a non-MB question but the concepts should be universally applicable. I have an 87 Saab 900 with a 2L 16V engine with 211K miles. Over the last 20-30K, oil consumption has suddenly increased from zero added betweeen 3000 mi changes (at MIN at change, down about a quart) to nearly a quart per 1000 mi. There are no leaks of significance. I know the oil is going out the exhaust as I can smell it and others have told me so though is isn't nearly bad enough to see in the rear-view mirror. This engine uses a Teflon/ steel-spring valve stem seal that no one ever routinely replaces (even though they come with the head gasket set) because they just don't fail very often. This engine is also known for never having lower end issues unless subjected to lack of lubrication or severe overheating. I have no reason to think either ever occurred with this car. I bought it from the original owner who had every service receipt from day one and clearly took good care of it. My compression is perfect and identical to that seen shortly after purchase 60K miles ago. The plugs are uniformly covered with a tan ash-like deposits. I'm told it smokes under load and on overrun. I've never had someone drive it while I observe to more definitively determine when it smokes but I'm going to.
So, is there any definitive way to rule in valve stem seals or is there just the process of elimination, fairly definitively ruling out everything else? It's not that big a deal to pull the head and replace them and do a valve job but I'd be very disappointed to still have the problem.
Thanks in advance.