Ok, so it turns out that you can't tighten the slotted nut enough with the screwdriver to make it seal well. After a week sitting at the paint shop getting the hood resprayed, most of the refrigerant leaked out (even though it didn't leak down under vacuum).

Me and my grandpap came up with the idea to use an allen cap screw a couple sizes bigger than the 1/4-20 that the stud was to hold it in. We cut off the cap screw, drilled through it, tapped 1/4-20 threads into it, and then turned the head down some to fit in the hole on the expansion valve, which we enlarged slightly to 1/2".



The cut off end got cleaned up after the picture.




This lets you tighten down the broken off side just as much as the other side.


We also decided that the side of the expansion valve wasn't machined well enough (not surprised being it's an aftermarket part), so we used some 500grit silicon carbide paper on a flat surface to smooth it out. You can see it wasn't perfectly flat before apparently. Those deep radiused groves were across the whole face of the part.

The marks on the upper part of the picture were across the whole surface of the valve, and you can see the part apparently wasn't flat either.