your pics:
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You can probably go to Lowes and get some red rubber gasket material (in plumbing) and some rubber cement, and fix it. Cut a pieced of the gasket material and glue it to the inside of the 6" PVC between the pipe wall and the feeder.

OR

If there's enough room, and if the bottom connection is 3/4" female pipe thread, you might can fit a Fluidmaster brand float valve in there. (Plumbing, again.)

OR

Maybe if you remove the actuator (turn off the water to it first) and examine it, you'll find it will work just fine with 1/4" of stuff removed from the side that impinges against the interior pipe wall.

Ben