Welcome to Team Talk.
After cleaning out the bilge, I would refill the trans. and run it again to see where the leak is. Should you need to pull it to replace seals, it may be worth rebuilding as long as it is out already.
I'm kind of partial to '77's. How about posting a few pictures?
Two 14" 5 lug S5 wheels with ST205/75R14 Kenda Loadstar radials $349
Two 14" 5 lug S5 wheels with ST215/75R14 Kenda Loadstar radials $389
Two 15" 5 lug S5 wheels with ST205/75R15 Kenda Loadstar radials $409
Mounted, balanced and delivered.
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CARBURETOR REBUILDING - $199
Parts, labor and return shipping included
2 LED 6" BRAKE LIGHTS DELIVERED $32