Oh Lordy, I now own a Fordy (a Lincoln actually)..

[roadster]

The plastic piece is seldom seen probably a Lincoln item for protecting the o ring behind kick down lever and am sure it came with the split or crack . There is a small o ring on the kick down shaft they didn’t leak very often and very easy to change , if you remove nut holding lever to shaft the o ring is behind plastic piece. If car sits for a week or longer the converter starts to Fill the transmission more and more that is why so common for automatics to only leak after sitting extended period . Factory used cork gasket dry just want to make sure pan rail straight from over tightening pan bolts over the years (torque to 16 ft lbs) The kick down shaft contacts valve in valve body past 3/4 throttle or so and only moves 1/2 inch or so is spring loaded . Those are neat cars , friend of family bought new 2 door like yours , except his was a 74 give or take a couple years .