Are the sending units really dead?
Mine was fine... it was the float that got filled with gas due to a nearly imperceptible crack.
Soldered the crack after letting the gas evaporate out, and tested it in water to ensure it floated and did not get filled with water. It passed.
I checked the rest of the sending unit over and it's good. Measures fine across the whole scale.
Unfortunately for you, if the floats were full of gas, it would've evaporated long ago, and seeing the gas come out of the float in a certain spot is pretty much the only way to tell exactly where you need to seal it up.
Check the resistance across the entire range to see if it's reading right. If it is, then the float is the problem. I'll check my sender again and post the top and bottom resistance readings. There should not be any 'glitches' or dead spots in the range. It should steadily increase or decrease, depending on which way the float arm is traveling.
In your case, I would find an old pan at Goodwill or the Salvation Army and melt some solder in it, then dip the float in, one end, let it harden, then dip the other end. Cover the whole float with a layer of solder to seal it up.
1996 Ranger 3.0, 5 speed stick, 4x4, 3.73's, 31" BFG AT KO's
Wiring, it's all fun and games until you poke yer eye out with a soldering iron...