It does sound like steering lock failure, have you tried jiggling steering wheel up and down or tapping the lock, sometimes this will free it up temporarily according to the US forum.
Not sure I've noticed anything - can you elaborate on what tyre scrubbing means Will?
In cold weather turning on full lock at low speed the tyres feel like they running over pebbles.
I paid Abbey to do all of my S/c work and it came to about £12,000 in total for the 370.
GTM supercharger: 432@the hub and 367ftlb torque with standard pulley giving 7.5 boost