I too have repaired a fuel sending unit. In my case it has been on a 1971 VW Karmann Ghia. The issue I was faced with was a gas gage that had a spot where the needle would jump around from a full reading to an empty reading. As it turned out, it was a combination of corrosion on the float contacts and on the resistance wire. Using 1000 grit wet/dry paper cleaned both and the gage worked fine. The float on this vehicle is very similar to the BMW float in Rob's article. Be very careful in cleaning the resistance wire. It is very easy to deform it where it is no longer straight.
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