For some time Winnebago has been using their version of the SeeLevel system. While it does not have the digital readout (only gives 1/4-1/2-3/4-full), it does have mass sensors mounted on the outside of the tank rather than the through the wall pins that get fouled by tank debris. Do the GEO method with a small bottle of dawn and calgon water softener. Fill your black tank 1/2 full of water and drive some curvy roads to slosh things around. With luck that will clean off the sensor and get your monitor working again. Best chance to keep it working is to never dump the black tank until it is almost full and be sure to dump 2 bowls of water after each "deposit" in the toilet. Lots of water is your friend. Makes for a more forceful dump that is more likely to carry stuff off the sensors.