Nithmo

I would fight the dealer, and I would escalate it. Keep climbing the rungs of management. Start with the service manager, then general manager, then dealer owner. It may not be easy to find the dealership owner's contact info, but don't hesitate calling if you do. In my experience, you eventually get to a level where someone simply doesn't care anymore and will approve the repair, without you having to pay.

Even if you get nowhere with the owner, I'd call Nissan customer service and keep escalating the issue.

They are calling it "wear and tear" on a part that is well known to fail prematurely. Also, pushing a clutch pedal in and out results in wear and tear on the clutch and eventually the flywheel (if the clutch is completely worn out). Those two are never warranties and understandably so. There is NO wear and tear that happens on the CMC or CSC. It's a cylinder that slides in and out based on hydraulic pressure. It's just a poorly designed part.

Me thinks is they're pushing you off on something they know is an issue and are telling you to pay for it. How isn't that a warranty claim?

Personally, I'd try making a deal with them. Tell them you don't want the same shitty parts and that you will provide better parts, as long as they provide the labor. Also, indicate you expect no warranty on the new parts whatsoever, since they're not theirs. That way, they really have nothing to lose.