[MT-2500]

4 speed overdrive that year will be a 700R4 transmission.
The 84 year transmission is a weak transmission to start with.

From what you are telling us it is a dead duck.
Seal leakage is usually caused by deeper problems.
That you need to repair before seal will hold.
Pump can usually be rebuilt at not much cost but how is the converter?
But How much internal damage do you have?
Is front seal blowing out or just leaking?

You are already dumping money and time into it and not getting it fixed.
If transmission not shifting good it is more or less internal problems.
If seal not holding it is bad pump or converter or transmission slipping internal and causing transmission fluid to heat up and blow out front seal.
Seal leakage with sipping/not shifting right?
You might as well replace it or rebuild it next time you have it out.
And be done with it.