After installing our granite counters, our granite guy had to return and drill a hole for the air valve since it's required by code for the dishwasher. Unfortunately while doing so, he measured incorrectly and managed to only drill half-way into the pre-cut holes on our cast iron under-mount sink and the other half of the hole bit hit the rim of the sink. We probably wouldn't have even known about it had my wife not asked him about the iron stains in the sink, since it was new. He then admitted that they were from hitting the sink with the bit and shaking it out in the sink and that some Barkeepers friend would remove the stains. He also left the core from the granite in the sink as well, which got me fairly upset. After contacting Kohler about the sink, they told me that the warranty would now be void since drilling into the cast iron can cause rusting and may eventually crack the enamel. Needless to say, I was angry over the carelessness and also noticed that the plumber had to then shim the air valve since the nut for the bottom of the valve only sits on half the sink hole and cannot sit flush on the bottom of the counter as in a proper install. Anyway, my contractor and granite guy have both reassured me that they stand by their work and would guarantee it themselves and in the event of a problem they would fix it. My concern here, though, is if they are no longer in business if a problem does develop down the road and the sink is not underwarranty, I'll be left holding the bag. I'm also concerned about having the shim on the air valve and if that's now more susceptible to water getting in under the counter if the valve does backup and more susceptible to rusting. Anyway, I would appreciate any well-informed advice. It sickens me to think about having to replace the granite if needed since it's a fairly unusual shade of Venetian Gold, as well as the undermount sink . I'm also concerned that replacing granite may end up damaging counters or floors since it's a new build.Thanks in advance.