There's more to it than that, really. My dad had a warranty claim on the 302 in our old station wagon & the dealer said it was owner neglect. Dad never drained oil from the front plug (there are two drain holes in some 5.0 motors) on the oil pan & they said sludge caused the engine to seize & it became my parents' responsibility to prove otherwise. In the end, they shelled out 3K for a new engine. The dealer only has to show that your mod 'might' have contributed to the problem & then you have to prove them wrong. For example, take your long tubes. You could develop some engine ticking & take it in for repair. The dealer tears the top end down & says you've got some valve problems (or something like that). Then they say it's because the non-stock exhaust headers created a different backpressure than the engine was designed for which damaged some of the exhaust valves, hence the ticking & therefore, it's your problem to fix, not theirs. I'm only making this up, but you get my point.