Here's a pic of the flip-flop valve. The bracket attaches to the back of the trans. so the valve sits on top and to the rear of the trans case. If you remove the small steel pilot line that connects to the fitting that's at the top of this pic (right side when mounted on tractor), it shouldn't drip or leak excessively when the tractor is running. "Leak excessively" has never been quantitively defined but that's the criteria they use to determine if it needs replaced. Don't put the transmission in reverse when the line is off or it will really squirt fluid.
My 75 was making transmission oil and I didn't feel like shelling out $800 for a new valve that would likely start leaking agiain. Solution: remove the valve, plug the fittings for the pilot lines at the trans, and make up and install two hoses for the steering. Tractor now steers different when in reverse. Not that hard to get used to.

(flip-flop.jpg)

flip-flop.jpg (87KB - 435 downloads)