Mine's still keeping mileage at a reliable rate. I took it on a highway run recently and for the first time ever, it actually reported the correct/known mileage for the trip.

One thing I did differently than you was the O-ring. Yours fitted inside the plastic cover and pressed on the end of the shaft. I didn't have one that small, so I fitted mine over the end of the plastic shaft, so it pressed on the plastic cover. *edit* should have looked up, it was a 5.5 x 1.5mm

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]