My guess about possible "spring damping tension" was nonsense - due to the lateness of the hour, sorry.
Is the "30 degrees of slack" 30 degrees at the wheel
or at a rudder? Makes a big difference.
If there's slack and the the helm unit has been dismantled is it possible that the 3 shafts on the outer casing didn't engage in the 3 planetary gear
bushes on reassembly? That would obviously cause extreme slackness. Worn planetary gears, shafts, bushes might possibly cause 30 degrees at the wheel.
In the vimeo the helm unit mounting bracket looked a bit flimsy.
Cables inserted into the helm unit at the wrong point of the circumference would restrict wheel travel and create an angle between rudders - but no slackness I think?
If you lock the wheel and check each rudder for free play that might tell you something, especially if a cable is broken or disconnected.
"can BOTH cables be run into the same side of the dual cable helm ,as done on twin engined powerboats , and to compensate for this , one of the rudder quadrants is turned, through 180 degrees ,therefore both rudders will be pulled then pushed at the same time , instead of one pushing / one pulling ?"
The helm unit does appear to have been designed to be able to be used in either configuration but I don't see what is gained by changing it?