Thanks for your advice people, AIS fully removed today. No probs using M8 tap, I actually had a tin of metal cutting compound, so I kept dipping the tap in that, job done. Went for a test ride after, and all is well apart from a crackling sizzling noise which I've only just noticed when the ignition is switched on. Sounds like something arcing or shorting out, but just been searching the forum and apparently it points to the servo motor. Hope it's that, but not noticed it before.