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That tiny lip of the valve stem seal is one of the most important seals protecting the engine from carbon deposits and the catalytic converter from being contaminated. The valve stem seal can fail two ways. First, it can wear out due to the movement of the valve and tough conditions inside the engine. Second, installation errors can cause the lip of the seal to be damaged.
Doug Kaufman explains what this means if a valve stem seal is damaged. This video is sponsored by MAHLE.