I am correct in thinking that the dealer in question DID install some replacement / donor parts to this car ?.
Of course MG CS would have been the driver in suppling / authorising the replacement of these parts.
Gone are the days when dealers are just allowed to fire the part cannon and order what they like anymore.
I was told by a senior tech at a VAG dealer, if they order items under warranty and install them without the consent of VW first, if the part is returned under warranty to VW and is found NOT to be defective, they reject the warranty claim and charge the coast back to the dealer.
We have to remember, if the dealer had identified the problem as being simple, then it would have been a quick agreement from MG CS and its all sorted.
The dealer was not going to spend many many work shop hours trying to diagnose the problem, to be then told by MG CS that they would not be picking up the tab for the work.