Hey sorry to hear that. After 120,000 trouble free miles (and one fluid change), I had the same symptoms (but without the noise) with our 1997 C230. Our independent mechanic that we use for normal things tested electronically (and, I think, just as important, visually and smell wise) and ended up installing a new valve body (and one other minor thing I can't remember) and all was well. The work included new fluid and filter. My understanding with the 722.6 is that it's fairly simple to figure out what's wrong and, while not inexpensive, fix it. Hope things work out for you.

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Michael

1988 300 SL (5 Speed)
1994 E320 Wagon
1997 C230