Thanks for the replies guys, all useful information, I am at the stage of deciding who to use for my next issue, a corsa transmission control unit as the company I usually use has carried out a repair on a control unit that I did not ask for (requested as part of immobiliser set) and returned it faulty when it worked ok to start with. I returned the unit for test and was charged an admin fee (return postage) and guess what, on refitting it worked ok !

I agree that sometimes, either replace or advise, customer to go source a used part and " on their head be it should it not be a quality one".