My H310 has a stock 50 gal. holding tank, with the needle stuck on 3/4 full. The level sensor is original, a plastic sending unit about 1.75 dia. x 10" perforated with holes the entire length. Inside there seems to be some kind of float that is free, but there still is no change in the tank gauge indication. Is there anything I can try, like checking the resistance of the sending unit, to see if it is correct, or at least a manufacturers replacement part number. There aren't any part numbers on the unit Thanks for your help. Ken