Not sure where you are going here, but tvat sender is easily repaired. The how to here on fabo details the procedure.
As for aftermarket senders...
If the sender is not tuned to the guage AND the tank it will never be accurite.
If your aftermarket sender is tuned to your aftermarket guage it should read fairly accuritely. Only the shape of the tank is the variable and after the first 5 gallons or so the tank is fairly liner.
