'How willing are the OEM suppliers to settle such claims', Well, VAG and BMW want the cars in their workshops for diagnosis on any failure of their parts and if there is any consequential damage as here, you don't need to be Einstein to figure their response- incorrect fitment etc etc.
Warranty is all a bit untidy but stick with it Steve-keep a note of all the time you are spending resolving this and next time tell them up front that it will be part of your claim against them,
Perry Mason
AKA Ed Kaps