I've had Pentax SLRs since 1967 when I bought a Spotmatic. Since then I have had K1000, ME, ME Super, K10D and now K20D. For all I have a range of lenses, and still use them all. In all these years no warranty claims were necessary, until the seal strip came out of the 16-50 2.8 zoom, and the autofocus failed. I was shocked when Pentax refused the warranty on the lens, claiming it had been dropped. When I asked for proof they sent a photo of the inside at the back, which clearly showed the problem: One mounting screw had been over-torqued, probably in manufacture, because the mount must be removed to see it. The screw fractured its mount, and slightly warped the lens case, causing the failure of both the seal and the autofocus. With the photo came a new claim, that the lens had been on the camera when it was dropped. Donkey-dust.
Neither the lens nor camera has suffered any trauma, and there are no marks on either that would indicate abuse. There is only a severely overtightened screw inside the seven-month-old lens. I guess its time to move on to Nikon, with a much better engine, far less image noise and a warranty that can be trusted.
PS I was also responsible for the purchase of more than 800 k1000s, MEs and ME Supers during the '70s and '80s while teaching a course in composition.