Have you tried an anti-bacterial spray?
https://mr-blacks.com/shop-global/uk/denim-refresh.html
I can vouch for Mr Blacks... very good stuff indeed... it's a tad Febrezze to start off with but gets rid of that 6 month stench
@Johnnyw75 started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
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Have you tried an anti-bacterial spray?
https://mr-blacks.com/shop-global/uk/denim-refresh.html