Well more adventures of the uneducated, but we learn by our mistakes, right?Well my mate has a bike, & I decided to practise on it!
The bike has been used fairly heavily without a service all year. The chain had 4mm of wear so the cassette will need replacing along with chain & may explain ghost shifting.
On closer examination the crank's axles through BB seemed to have a lot of play, after trying to get cranks of with a rubber mallet, it was clear I would need a crank extractor. It turns out the crank/BB is of the now obsolete square taper variety. Thankfully my brother has both an old style extractor & spare BB cartridge which he will post. So a new Deore 11-32 9 speed cassette & SRAM chain should set my mate back just £35 & he'll be good to go.