I found one rear tire (left) had gone completely flat while the car was in the garage. I think it was OK when I last drove it, probably picked up a nail or something from our rough gravel driveway. The car is old but not driven a lot, this tire has lots of tread and looks fine but it's old, date code is 2206 (2006). No visible cracks or aging. Should I get it repaired, or replace both rear tires? (The front tires are newer.) I can't be absolutely certain I didn't drive on it a little ways, but I doubt it. These rear tires (Kumho) are a wider than usual size (245) which is hard to find (and expensive), for performance, but I don't drive it for "performance", I'd replace with same size as the fronts.