The tank sensors in my tanks are solely terminations of electrically conducting wires. There is one live sensor at the bottom of the tank, IIRC, and 4 grounds at the various levels; 1/4, 1/2, 3/4, and Full. The liquid just completes the circuit between the live and the various grounds, and the lights illuminate in the panel. If, for example, the tank is 1/2 full, the Empty, 1/4 and 1/2 lights all illuminate. If yours were the same, the sensors are very simple, and I ordered replacement sensors from my local Airstream dealer for a few dollars. You would probably need to order them for a later trailer, like mine, rather than yours, as any catalogue would probably list yours as "unobtainable". They are designed to be glued into a hole drilled in the tank, and they are in the corner side wall near the outlet. They are very difficult to keep clean and operational in a black tank.
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."