Simon,

we had one do this down in Wollongong. Tates tried to glue it back in (twice I think) but it just popped out. I took it up to Japan and sent it over to Yamada they replaced it no charge (in fact they supplied the whole head assembly with all the valve gear) Eventually Tates also replaced it so we had a spare head in the club. If you have no joy with YS Performance I would just put the head in bag and send it to YS. If you have any questions PM me.

Brian