Thanks cn and erik
Found the plate removal thread and it might be hacky but it sounds a lot easier than messing around with shear bolts! Will definitely be trying that first. Appreciate the detailed write up cn.
FWIW I found an unused Volvo tumbler/key set on ebay for £30, so anyone in need might do ...

Hi I've just acquired a 98 V70 and it has a similar symptom to this - intermittently sticks at Pos 0 and needs a wiggle (understatement) on the steering wheel to allow the key to turn to the next positions. Can anyone confirm if this has the same cause? And will replacing the cylinder sort it?