@Stevie,
I was in the same position a few months ago. After 2 1/2 years of problems my SEAT was inspected by the RAC who recorded several faults. The car went to the main dealers but they could not find the faults in their workshop. 3 months – yes, 3 months it was in the garage before MB decided that they would reclaim the vehicle and place me in a hire car for the remainder of the lease.
Whilst seemingly a good position, every time there is a minor issue with car e.g. needs a service. The car needs to go back and I have to push for a suitable vehicle. Whilst the SEAT was in the garage I had a Toyota people carrier which drank fuel and ad blue. This was then replaced by a Merc GLB quite nice but a lot smaller than the scheme vehicle. Certainly can’t get a dog and scooter in. Plus each time the vehicle changes I have to get it valeted to remove any trace of dog hair.
What I am going to do at the scheme end is still a worry as I need a biggish auto SUV, which as well all now are disappearing off the scheme or take 12 months to arrive.