There's no ratchet, as such, on a fixed spool reel. Do you mean that there's no audible click?
What I'm struggling to understand is the fact it works perfectly when the baitrunner is engaged
I have a Shimano baitrunner Aero.
The audible click is made by a finger inside the spool that runs on the cog on the centre spindle of the reel, try the spare spool to see if works
Well done.:thumbs: put the other spool on and it worked perfectly, but examining both spools closely I could not detect why one works and one doesn't. Putting the spool on the reel upside down provided the answer. It is indeed wear on the finger, so minimal (a few thou) but enough not to engage with the cog.
Can you spot the worn one?
Wonder how easy it will be to get a new finger from Shimano, my next task.