I have a 1991 350 SDL with same engine ... mine appears OK at 150K, but I hate the statistics of this particular engine.

The only odd thing occuring on mine thus far was an occasional "miss" at highway speed after extended operation with a collateral puff of brownish smoke ... during a replacement of the glow plugs, I removed the intake manifold and cross over pipe, noted incredible amounts of carbonized gunk from what everyone believes is an EGR valve that is located to close to the valve cover rebreather intake ... i.e. oily fumes from valve cover exhaust meet hot air from exhaust and you have "carbonized gunk" (my term) that I think was being pulled into the combustion chambers and exploded with the fuel air mixture ... while there is no evidence to conclude this is directly related, to me it at least seems reasonable ... I had the intake manifold dipped several times and still had to clean it out with mineral spirit soaked rags to get the gunk out (some gunk is normal) ... the cross over was at least 40% blocked, BTW ...

As noted, my SDL is a joy to drive with mega mileage ... heavy, smooth an d confident handling. NOT like an E class, though, in handling department.

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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg