I wonder if you can use a plastic repair kit to make a new one. Car shops, hobby shops, some other types of places might have them. In Sweden I don't know of any places lol.
Use the old stem cap for the exterior mold, just use a 6 mm wrench end to make the fitting bit. Paint silver when done.
cdr
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"...during the Lance years, being fit became the No. 1 thing. Totally the only thing. It’s a big part of what we do, but fitness is not the only thing. There’s skills, there’s tactics … there’s all kinds of stuff..." Tim Johnson