Fuel Injector warranty extension and consequential damage

[d.b]

My '14 M5 has been at a BMW service center since the end of September. I brought it in because it was getting progressively hard to start.

The tech did a diagnostic, boroscoped the cylinders and said that the cylinder walls were scored, and the engine needed to be replaced (damaged by the faulty injectors). He said that the engine would likely be covered as consequential damage.

Some time later, after replacing the injectors and spark plugs under warranty, he said that the cylinder walls were not scored, and that it was likely carbon buildup that he saw while scoping them. I asked about that portion of this story earlier, and learned that this is not how carbon builds up...

In the meantime, he also fixed a turbo coolant line that was broken, and told me that the engine probably does not need to be replaced (because the walls weren't actually scored)...

Upon firing the car up after they considered the service complete, they noticed coolant coming out of the exhaust, indicating that there was a blown head gasket. I did not find out about this part until I called and also learned that they had an ongoing PUMA case in order to get the engine replaced under the __previous owner's__ CPO warranty (CPO warranty is void unless private to private sale - which my purchase was NOT). BMW was set to have the engine swapped, until they learned that the CPO warranty was void, at which time they rejected it.

I spoke with the service manager after this, and told him about my concerns regarding the "carbon build up" on the cylinder walls and asked to have them scoped again to find out if they actually were scored or not, which he agreed to. About a month later, I finally got an email from the service advisor saying that there WAS scoring on the cylinder walls, and BMW had agreed to pay for 50% of the engine replacement.

My question is - If the fuel injectors were bad, and damaged the cylinder walls to necessitate an engine replacement (at the first diagnosis), then why would they not cover it completely? should they? is it a fair offer?

On another note, communication from the service department was piss poor as well, and I had to email the dealership GM just to get a meeting with the service manager after multiple emails went unanswered from both him and the service advisor, and months going by between communications about status etc... I sorta got the hunch that they only reached out to me when they realized I was still in their loaner car.

Any advice is appreciated.