The only reason I suspect it's motor oil that is getting in, is because the system is a closed system, except for the point that it attaches to the head, what other source would cause the level to rise?. This level change has happened over the period of 1 year and 4 months. Though I suppse if that o-ring was bad, I would see leakage between the punp and the head itself. Since the parts in this system are expensive, I just want to head off larger ($$$$$$) problems, if I can.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

I just got back from the dealer. I had to buy some replacement valve cover screws for the 1988 300E as I managed to overtorque them and snap one over the weekend while replacing the gasket ,and I asked to look at the hydraulic pump set up with my 190E 2.3-16 on their microfiche reader. I looked at the shaft sealing arrangement and it was pretty simple. All the seals cost less than $20 for that car.

Anyway, there are a pair of "o" rings, a paper gasket and a shaft sealing ring. One "O"-ring is $4.00 and the other is under $2.00, while the paper gasket is about $1, and the shaft sealing ring is $12 or so. They are all outside the pump casing proper.

I would assume the set up on the TD is similar, and likely uses the same pump. I did not ask about a repair kit for the pump, but I don't really think you need to fix it unless it is not working. The oil ingress is not necessarily a "pump" issue. If the pump was leaking hydraulic fluid that might be another matter. Hope this helps, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)