OE seal from a dealer runs about $80 discounted, and forget aftermarket (ie. worldpac) seals because they dont fit well at all and possible leaks will result.
Don't be so cheap as to risk turning your car to a rust bucket by saving a few bucks on a seal!

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!