@pigeon Just checked the returns page for them. Must have been under 30 days for my friend as they'll take it back and handle it then. Otherwise it's back to the company :/
Stoke Solutions is the only one I'm aware of but I've heard mixed reviews as of late. Onewheel are selling parts now though so give them a poke as they may be able to diagnose and ship out a replacement part under warranty.
If all else fails if you're near Towcester I could take a look.