the car was brand new in july it has the 4.8litre engine
Sorry to hear that you are having problems Scottie, as Cereal suggests I would give the Dealer a specific written period to solve the problem. If that does not do the trick, then I would certainly get in touch with the works personally and get them to sort the problem once and for all.
If you need details of who to contact, etc, at MMC please PM me and I'll put you in touch with them.

I am sure that you can get it sorted and then enjoy the car, as you should have been able to do from Day 1.