Battery has a dead cell I'd expect if you are getting 9v on crank. Might be healthy until a load is applied, surface voltage isn't a reliable test.

Certainly isn't. As a lead Acid battery ages, it develops resistance and from ohms law, it will drop voltage across cells in the battery and consequently the off load voltage will be a lot more than when battery is asked to work = turn over starter.

I just thought that I would post an update on this.  

I whipped the starter motor out again and whilst it was on the bench, did the three tests of 1. solenoid 2. motor 3. solenoid / motor combined.  All worked absolutely fine and after running the tests several times with no failures, I put it all back together again.  This was about a week ago and since then there has been no repeat of the clicking and it has started first time, every time!  

Perseverance seems to have paid off.

 

Many thanks to all who contributed to this thread.

 

PS:  Dipped beams have stopped working tonight!!!!  - I may be back!

Headlight problems can often be caused by the switch itself, simply push the knob in, twist clockwise and pull the whole thing out so you can continuity test it, replace the whole unit if it fails the test.

Sticking starter hit it with a hammer

Or just get a 2nd hand unit