Gas Gauge on E.

Hello guys. I recently purchased an 05 Chevy Aveo from a used car lot with the dealer not knowing anything about the car. I managed to get a pretty good deal on the car but noticed it has a lot of little things wrong with it yet it runs really well. The gas gauge hasn't worked and right away I figured the sending unit was bad. After replacing it the gauge still hasn't worked. While changing it I noticed the wires on the harness all had the insulation worn away. So I went to Pull A Part in my area and cut off about a 2 foot section of the harness from the connectors. After soldering them in and heat shrinking I still haven't had any luck. The gauge I'm assuming is working as this has the temp on one side and the gas on the other. The temp side works fine. Everything seems to point to a ground wire being a problem. The tank being plastic I'm figuring possibly to locate the ground on the harness and splice in another wire and run it to the seat frame possibly. My question is, the sending unit has 2 harness connectors. Do I need to find the ground on each connector and try to reground it or does only one connector run the gas gauge? All my fuses and relays by the way have been checked.
And if I'm allowed one more question; I noticed a small pin hole leak in the radiator. Small bubbles coming out and drips. Is there a good sealant that is sold at the auto stores that will fix this hole other than trying to re-solder? I heard the JB Weld doesn't last either?