Bob your pump is leaking, there are actually two seals, the one next to the fan drive tube is the culprit. My 70 gas std. had the same problem.
Sure as I tell you it can not be fixed on the tractor someone will say they have done it so I will not say that. My recommendation is to remove the two bolts holding the radiator and move it forward about two inches (as far as you can) then it will come out the side. Plenty of info on what you will encounter and how to guidelines from guys who have done this job.