so my front tubeless tyre went down last night, pumped it back up but air was seemingly escaping from one of the spokes!

I thought that the rim was competely sealed from the spokes.
Are 819's known to fail in this way?

(admittedly it was dark, cold and outside a pub, so didn't investigate it for too long – tube went in, cider was consumed)

They should indeed be completely sealed, the spokes don't fit in the same way as a tubed rim, they have to be put into the little cups & screwed in from the hub side of the rim if you like. Wants investigating if it is leaking from a spoke hole

It cant…

Sure its not the valve – and have you any latex in?

Check the valve is seated in the rim cleanly and also not either cracked / broken or clogged up with latex.

ok, will check again at the weekend (in light & dry conditions), definitely seemed to be out of the spoke, & had latex in it – hadn't needed to mess with the valveand it was a bugger to remove, so I thought it was well sealed.

i had something similar with a 819 rim with air escaping for no apparent reason. after tightening up the valve and pumping it back up it has since stayed inflated.