It would be near the top of my "do it soon" list. Mine seeped for about 3 months before I got around to changing them.

If they do fail suddenly, you will loose too much oil fast. Drive with one eye on the oil pressure guage.

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html