3 days of driving slouhd matter that much unless you drive hundreds of miles each day. And with one being a spare, I doubt you did. Anything over 100,000 miles slouhd not be covered under warranty. This is why the warranty is not stated as covered until 105,000 miles. There has to be a point that the coverage is stopped and you have exceeded it. Just bad timing on your part. The rear end was probably on its way out to begin with and you just finished it off. It is not a good practice to run different size tires all the time as it can cause some premature damage over a long period. As for the 1 new tire and the rest worn. This slouhd not void the warranty on the rear end, nor will it damage the rear end. Tires wear that's what they do.