Bikes been playing up with symptoms of a flat battery.
Battery has just been drop tested & passed.
Battery at rest:- 12V
idle:- 14v
5k RPM:- 14V
= charging system (for once) is not the issue.

which leads me to the starter relay...
Can you use a NC23 starter relay on a NC29?

Probably Yes, to quantify, ive used a vfr750 starter solenoid on my nc23 and it was ok. its probably the same part number for a fair few hondas.

The only thing i could add to this is check out before you buy that the leads will fit. I seem to remember the leads have an angle type of connector on the positive side and will not sit right if its not got the cut out for the connector on the solinoid. I know i tried a cbr125 type on mine as a test to see if mine was faulty.

cheers, i think i am going to wait till payday & get a new one, bike is about to run out of MOT as it is & needs more work doing.
I know i have never changed this part in the 13 odd years of owning it.... i do know the starter motor & battery have been changed in the last 5 years!

Instead of just replacing it.. it cost me 3 bags of Do-nuts at my local Auto Electricians to test the starter relay...
which passed just fine..
BUT they have said that it could be the starter motor its self.
They know the history of my bike as they deal with it when i cant.
just over 5yrs ago i bought a 2nd hand starter motor off flea bay & brushes etc from Honda. Auto lekky guys re-furbed the starter motor + put a years warranty on it.
Honestly thought the motor would have lasted longer than 5/6 years, but no telling how worn out the donor one was.

starter motor off & take that in to test it..