I used a 1 7/8" wrench to remove the sending unit on all 3 of my 123's. Used very little effort to remove the unit, the wrench is 2 ft long Spray some brake cleaner or carb cleaner in the little hole and shake and repeat. The low fuel light finally works on all 3 cars.

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'83 240D 264k on 100% biodiesel/ 31mpg
83 300D 217K the $800 gem
'82 300D 267K the new WVO project car finished and driving for free
International tractor B275 on B100
Ford 555 backhoe on B100
Sargent 25 ton Rough Terrain crane on B50