Replacing the sender should give you "new" reliability. Getting the odometer fixed properly at a speedometer shop is about $80. Not a good candidate for DIY, unless you have experience and lots of patience. I carry a gallon of Diesel fuel in the trunk just in case.

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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles