A couple a weeks ago I took my 2000 A4 Quattro to have one of the Wheel Bearings replaced (rear). When I picked it up I had an ABS light. The guy told me it was because they had to take out the tire and stuff, that after running it about 50 miles it would go away. I've driven it more than 100 and the light is still there. I took it back and he said that it was the sensor. He said that is common to brake the sensor when removing the wheel. He said he would change it for free, but that I'd need to get it.

Is this really something common?
Do any of you know where I could get one of those sensors? (part no. or name?)

I will really appreciate your help!