(X-post /r/miata)Mechanics: Should the slave cylinder be replaced at the same time as the master and vice versa? The dealership will not replace my clutch.

Long story short, I had my clutch replaced shortly after purchasing a 2006 Mazda Miata at 79k miles. They replaced the master cylinder about a month later because it was leaking onto my slave cylinder.

I'm now 14k miles into the new clutch (only has a 12/12 warranty) and it has gone bad because it doesn't fully engage, causing it to slip at higher RPMs. I need to know if the slave should have been replaced with the master, because the dealership is refusing to replace the clutch and they are blaming me for driving it roughly.