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Looks factory. He might not be able to do anything mechanical but @Dammit can make things look nice :)
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I used a scratch marker, it was perfect. Or Just get any round piece of steel of about 6mm and sharpen it, a nail could do too. The X cut may grow after you ram the valve in, as in Dammit's pictures, a round hole is way less problematic.
Another thing that works for me is tightening the valve a bit more as soon as it starts hissing
Fine if you have a hole punch. I have many knives, zero hole punchy punchy.