But a warranty claim by it's nature is for bad parts.
I had a warranty claim on my rear calipers. There was a bad batch. I bought the new ones, fitted them, and sent the old ones back. I was credited in full once they had them back. TBH, I thought that was fine.
I do know of a situation where a 5 speed gearbox was supplied with only 4 forward gears (!!!) and that owner got a gearbox refitted FOC as Caterham accepted that was basic quality control.
Ultimately, I suspect it's all about discretion. And yelling a lot (metaphorically) helps in that regard.
Jez