[Ian21401]

I understand re your back problem David. I have recurring problems myself. I find that walking is the best exercise for mine, but we are all different.
Trying to do as I suggest is not the easiest of contortion exercises.
It is a few years since I needed to adjust mine after fitting a replacement valve. I must have obtained one of the last OEM valves.
IIRC the small clip locates over the cable outer and into a couple of slots on the valve body, one on each side of the outer, so trapping the cable outer. Releasing the clip from one of the slots releases the pressure on the cable outer enabling it to be moved slightly, either towards the valve or away from it. It doesn’t need to be moved much. Slightly too far one way will allow full movement of the valve to fully open but prevent it moving to fully closed and slightly too far the other way will permit full closure but prevent fully open. It is a very fine line between the two but there should be a point which permits full movement in each direction.
I do not recall there being more than one hole in the valve lever where the cable inner locates.
Best wishes.