So far, anytime I had to change the sender unit, I let the back end of the tank down, with a flat bar accross I turned the unit and then took it out and found them broken physically.  They had one of their legs broken.  So, I soldered a piece in there to make up for the long gap.  Put them back.  Its just not worth buying a new one when the old one is fine except the missing link.
Zoltan