Is the offending spoiler really hanging open 30mm...........that's a bunch, close to an inch! Did you mean 3mm? With a ship that has over-center mechanisms inside each wing, I would lock the spoiler in the bad wing and then adjust the link from the over-center to the spoiler. This rod has to effect the spoiler position. Take the bolt out and move the rod by hand to see what the spoiler does. When the spoilers in both wings are in over-center (closed & locked) and the spoiler caps are flush, put the wings back on the fuselage and adjust the rods inside the fuselage to where the Hotelier fitting easily snaps on the ball.
If one spoiler really is open 30mm.............something is bent, broken, loose somewhere.........find it before you fly it!
JJ