It is quite scary some of the numbers banded about for repairs nowadays,yes parts are very expensive for some models but for a corsa regulator I would try and source one from a scrappy,it is quite a common motor and should be readily available,I don`t know what the garage, who quoted you their price, charges for an hourly rate but it may be in your interest to shop around,say you have a replacement regulator and see how much they will take to fit it.Hopefully you can save a few quid.
cdc, November 2012
