My 260E is using 1 qt. per 200 miles if driven 70-80 mph, and will go 450 if driven 50=60 mph. Mileage is 132K. Would this be valve seals, guides or valve job? There is no leakage under the engine. I haven't checked the compression yet but the engine performs the same as it did at 70K.

Thanks

Dutchman