Work through the problem step by step. It bleeds at the prop valve but not at the wheels? Try cracking the union at the rubber hose to the rear axle. Or the brass tee on the axle, or the lines going to the wheel cylinders. Chryco is right, sometimes the rubber lines fail. Sometimes previous owners "repair" leaky rear slave cylinders by pinching off the steel line. If you don't get any fluid at the rear axle unions, then your problem is between there and the prop valve. If fluid comes out at the axle, then your prolem lies between there and the bleeders. Happy hunting!