Anyone have a cracked monovalve in either 300D-2.5 or E300D? (W124)

[Jeremy5848]

I would like to hear from any E300D (1995) or 300D2.5 (1990-93?) owners who have had problems with a cracked plastic body in the combined monovalve/aux pump (001 830 40 84). The part number is unique to these two models and is very expensive (~$500).



In early 2013, the monovalve in my '95 E300D started leaking due to a crack in the plastic body. I replaced it with a new one from The Classic Center in Irvine, California. A couple of months later the new one cracked and leaked. It was replaced on warranty by The Classic Center. The replacement lasted another month or so and then it began to leak.





This is a puzzle. The monovalve is mounted on three flexible rubber stand-offs; there is a minimum of physical stress placed on it. All of the connecting hoses have been replaced as a precaution. The plastic body of the monovalve has no recognizable markings. The metal body of the monovalve is marked "Bosch" but whether they made the entire component or just the electrical parts we do not yet know.

Next, I went to my local dealer, Mercedes-Benz of Santa Rosa, California (MBSR). They were very supportive and ended up replacing the monovalve themselves at no cost to me. This eliminated any errors that I might have made. The third replacement lasted a couple of weeks and then it too cracked. MBSR and I decided there was no point in wasting time replacing the monovalve a fourth time. They have sent a report to Mercedes in Europe in the hope of finding some kind of manufacturing defect.

By accident I discovered MercedesShop member "chronometers" (Chris), who also has a leaking monovalve problem with his 1995 E300D. His monovalves crack and leak in the same place mine do. His first came with the car and the second he bought while on a trip in Germany.

I have been able to minimize the leak by keeping the pressure cap loose on the expansion tank but this is clearly not a fix. To provide additional ammunition to my dealer in their work with MB in Germany, I'd like to hear from other owners of this same part, limited to the 1995 E300D and the 1990-93 (?) 300D-2.5. Have you also had this problem? Have you never had this problem and think we're all crazy? Please let me know!

Jeremy