Well after several attempts "ten infact" we finally managed to weld a nut on and remove the snapped of ventalation valve
After we had welded a nut on nine seperate times the nut just kept shearing of when we tried to undo the ventalation valve with a spanner
Nut is place
snapped of ventalation valve removed
new ventalation valve back in place
cap back on
removed ventalation valve and the nine other nuts