i replaced the ball joint in my 89 hatch with just hand tools its very possible.
the tranny fluid isnt really pressurized so it wont blow a jbwelded seal but still id just replace the tranny. you should be able to get one for less than 100 bucks. i would NOT use any ATF stopleaks because more often than not they are bullshit and are really only meant to sort of revitalize gaskets, not actually stop cracks