Valve stem hole

Does anybody know the hole diameter on the Brembo rim to replace the valve referenced GU03617710, i guess it's a 10mm but i'm not sure. i suspect an air leakage located here as the pressure shut down from 2.5 to 1.2 bars in one month. I have replaced the old tire by a brand new one but i still have the same issue.

When I bought cast wheels (to replace wire ones); I bought these valves for the rims.....they are 8.3mm hole. Not sure if there are any variations in valve hole between wheels but they are identical on front & rear on mine (and I bought them separately & they are slightly different colour!)

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Have you tried just re-coring the existing valve? Might be worth a try before going through the hassle of removing the wheel and tyre again.