my 1984 W126 does the same thing, my front seal has not been done. i just got some lubro-moly engine saver (oil additive) to try. i may go with full synthetic next oil change. oil cooler lines are new, my vacuum pump rebuild kit is done, so this would not be it. could it be the seal under the power steering pump?

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1993 Mercedes Benz 300D 2.5 205K (ex wife's)
1984 Mercedes Benz 300SD 320K (SOLD)
2004 Mercedes Benz C240 75K
1995 GMC Sierra 2WD 5.7L 188K
1983 Mercedes Benz 300SD 239K (SOLD)
1987 BMW 325i 220K (SOLD FOR SALVAGE)

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