My step dad used to have a Vauxhall Vectra 2.5 v6 SRI as a company car in 2000, and the power steering failed on that. He noticed a noise and the steering going heavy on the friday, mum took it out to the hairdressers on the saturday, then on saturday night he went to pick up my bro from a discs, wasnt going fast as he knew something was wrong. Going down a country lane and came to a corner, at which there was a canal bridge, so he steers to go around it, but the powersteering failed, couldnt steer, then it kicked in, and he lost it, binned it into the bridge at maybe 35 mph and the car got written off.
Be carefull matey.