Well, finally after six months, I got around to correcting the inaccurate reading situation (no need to rush headlong into something so simple!). I ordered the sending unit that Jon suggested from renbusan on fleabay. The instructions that came with the unit are very clear, making it simple for anyone to do the install. The only issue I encountered was that the mounting flange was clocked about 90 degrees from where it should have been to put the float travel along the length of the tank. I corrected that by loosening the center terminal and rotating the flange to the correct position. For anyone doing this replacement--take the gasket and get it oriented in the right position,mark it and use it to mark the flange for correct positioning. I found that the mounting holes are not spaced equally around the perimeter of the flange, so there is only one way for the flange to mount.
