[askvictor]

Interesting. Though I'd argue that if the valve gets dirt on it, then eventually, when you unscrew it, some of that dirt will get deeper (particularly if you're completely flat and there's no pressure to push it out), and perhaps stop if from sealing perfectly. But I try to keep gear running for a very long time; this approach might be from cyclist who replace things a lot more often?

And yes, wheel reflectors are utterly useless.

[ehnto]

They are pretty robust, I have been riding the same presta valves on my mountain bike for maybe 5 years which I ride a few times a week, immense amounts of dry silica, muddy dirt, rain, cold, heat.

They are serviceable too. If you find it isn't sealing you can disassemble and clean the sealing surfaces, replace the locking oring or nut etc.