I suggest pausing for breath.
I'm not an expert, but in my view the issue here is not whether the car is out of warranty or whether you are entitled to goodwill from the dealer or MB.
You are entitled to a durable vehicle Under Section 9 of the Consumer Rights Act 2015.
Your claim is against the supplying dealer.
Given its perfect history a court is likely to find that your car was not sufficently durable and therefore not of satisfactory quality.
Goods to be of satisfactory quality
(1)Every contract to supply goods is to be treated as including a term that the quality of the goods is satisfactory.
(2)The quality of goods is satisfactory if they meet the standard that a reasonable person would consider satisfactory, taking account of—
(a)any description of the goods,
(b)the price or other consideration for the goods (if relevant), and
(c)all the other relevant circumstances (see subsection (5)).
(3)The quality of goods includes their state and condition; and the following aspects (among others) are in appropriate cases aspects of the quality of goods—
(a)fitness for all the purposes for which goods of that kind are usually supplied;
(b)appearance and finish;
(c)freedom from minor defects;
(d)safety;
(e)durable
You have 6 years from date of purchase to make a claim.
My advice to you would be to contact RAC or AA for legal advice if you are a member. Contact citizens advice bureau (I found them very helpful in developing a claim going through court now).
Do not authorise any work that involves you paying money.
There are megabux involved and you need professional input.
Hope this helps in some way.