>>>*The description really doesn't fit valve stem oil seals well as the culprit. Typically valve seals will cause the engine to pass light blue smoke at idle, coming down under compression, (like coasting down a long hill) or when the throttle is jazzed.

Plus unless the seals are gone or shot the engine still won't use a huge amount of oil, perhaps if a guide or two were very bad maybe. Very badly loose valve guides are a bit rare on this design, too.

The rich condition is the key here and the black smoke is an indicator. A rich running engine will use oil even when the rings are in perfect condition, this becomes noticeable on any long trip as "sudden" oil use since the evaporative system will draw out the lighter fuel molecules.

Overly rich conditions means fuel in the oil, the oil rings cannot control diluted oil. Plus remember you can take the oil rings completely off the piston and the other two rings will give close to normal compression. Thus a compression test is a good indicator of long term wear but not for upset conditions.

My best guess is the oil rings are weak, I say this because of the comment about running low a few times. The oil wiper rings don't last very long without lube, once they get overheated from friction, they will lose tension.

If I am right there is only one fix, replace them. Then fix the rich condition too.....*EB