Ok, so I took a big hammer to it, well alright a medium sized one, any tiny screwdriver as did as you say - the result was as you said. I did look in my stock of bolts, the biggest I had was 5/8" which didn't grip enough but would have done had the bush not been so worn - then again if it wasn't worn I wouldn't have wanted to remove it . . .
Before getting brutal I did test it out on the bench as a motor, it turned but really quite slowly. From memory when I did it before, back in 2015, I'm sure it turned very quickly. The battery I used was well charged.
It is now semi disassembled and I have added a new bush to my 'reminder' list with the supplier. I have a number of items on hold waiting for one to come into stock, delivery keeps getting put back - latest is 30th June.
So progress will be slow.
Thanks to all for your comments, much appreciated and even better helpful