Done it!
Took back off. Kept fingers away from Electronics and got a good hold of the spring....
1) extracted the components as shown in Plug's photo 1 from right-hand stick.
2) ratchet bar and screw moved from left-hand stick to right-hand stick.
3) small block with hook and screw fitted back into mounting on left-hand stick.
4) spring hooked onto centreing bar and then small hole drilled into bar and
small piece of brass wire super-glued onto centreing bar to retain spring. (see hook.jpg)
5) 2"-3" loop of stiff waxed thread looped through other end of spring
5 ) Thread fed through under gimbal from end with hinge mount.
6) String pulled up, two pins on centreing bar pushed into mount on gimbal.
7) Thread used to pull top loop over hook refitted in step 3.
8 Check stick movement and all bits sitting in the correct places.
9) Refit back of transmitter
Simples!
Richard