Good timing as my wagon began sagging a little over night recently. The PO had extensive SLS work done years ago, so the only SLS repair I've had to do is replace the resevoir itself. Darn thing developed tiny holes all over and began leaking. The resevoirs are dealer only and cost more than $400, so if you see a good used one at a yard or elsewhere, might want to pick up a spare...

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1982 240 D, 308,000 - 321,127 miles (sold)
1982 300 TD,166,500 - 226,000 miles
1998 E 320, 120,000 - 144,000 miles
2005 C 230 K, 26,000 - 77,000 miles (sold)