I have a 98' legacy outback with a set of kingstar tires that have approx. 20,000 miles on them. One recently was punctured and les schwab is telling me it's destroyed. They've also said that due to my AWD I'll need 4 new tires. Any advice on whether this is true? If not, how can I find an acceptable used tire? Also, should this be covered by Schwab's warranty?