I keep a spare in the trunk in case I need to change the oil on the road - about half of my trips go over 3000mi. Cleaning it when I get home saves time on the road.

On the OEM filters the part number goes toward the bolt thread. Better yet, look at both sides of the full-flow filter: one side has the raised sealing lip with a smaller diameter. Then look at the top of the bypass filter and at the bottom of the cannister housing head. You'll see which way the full-flow filter should go.

I wonder if the "forgot the full-flow filter" is a sales trick: oil pressure should go up if there's no full-flow filter and the bypass is rattling around.

Everybody knows you need to seal off the holes when you clean it and never use compressed air to dry. Right?

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daBenz - 1970 220D