And if it won't come out, the completely un-endorsed-by-NSR-world method, is to refit a washer and the nut, then use the claws of a hammer to extract the valve.

Worked for me, but I'm the gentle sort...

Here's mine before and after:


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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball