Six months ago, I went to an independent shop twice to have alignment checked. Both times I was told the alignment was good and didn't charge me. Today Costco removed a nail from front tire and their paperwork recommends alignment. The alignment shop put mirrors on all four wheels and I watched them do the check. They showed me the good readings. I'm a stickler checking air pressures so that isn't a issue. What is going on car drives fine? I took a penny to front tires and used Lincon's head to measure tread grooves all at same level plenty of tread. Could Costco be wrong? Should I get second opinion from another alignment shop? Tires are 2 years old Michelin Pilot Sport all season with only 15k miles.