Just walked outside and rear has a flat, no idea why, used the compressor to air it back up to 37, I presume the stock tires are run flats since there was white goo on the ground when I was airing up. Never had run flats before so do I need to get it replaced/plugged or can I just leave it alone if the run flat goo sealed the hole. If I need to replace it do I need to replace both rear tires or can I just replace the bad one. Car has 4K miles. Thanks for the help.