The problem is always valve guide oil seals. The labor by factory guide is 5.5 hours. It always fixes the problem unless you have a guide that is loose in the head. Such a condition is the only reason to do a valve job. BTW the valve job is rated at over 25 hours by the same guide.
Our procedure in cases where a large increase in consumption has occured is to pull the plugs and look for a cylinder in failure (significantly larger carbon accumulation on plug). We then do the seals on that cylinder first, looking for loose guides. If the guides are tight (as are usually the condition if the car has not been seriously oiverheated) then we proceed to do the rest of the cylinders.
It will solve the problem. It is possible that with a large amount of play in the guide to valve clearance, that the reseal will only last for 20-30k miles. Most cases it will last much longer even with guides at the wear limit.
Everybody always wants a valve job. I wonder if this is due to many shops with little experience or maybe they are just interested in the for sure fix and a weeks worth of labor. After all they will put in new seals so they are sure to fix the problem if they don't cause any new ones with major surgery.
Bosch Master, ASE Master, L1
33 years MB technician