They locked it because the clutch plate fell off and jammed the steering box.there are full clutch kits available, like this https://ttk-ac.com/en/a_c_compresso...nso_10pa17c_6pk_pv6_115_00_120_00_mm_mercedes, (it's just for example, i didnt find UK link)... are you sure that the solenoid is OK cos maybe they locked the clutch due to failed solenoid