Typically worn valve guides exhibit a puff of smoke when starting the engine when cold. With oil consumption being one quart in 3,000 miles, I would say this would be unlikely.

Best of luck,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles