Could be a number of things. Have the valve guide seals ever been replaced? How many miles on the engine? Soft valve guide and seals are among the more common problems for oil consumption on your engine. Do a search and you will find a lot of info on this subject.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record