My Model S is less than three years old and I always planned on purchasing the Extended Service Agreement (ESA) after my original warranty expired. However, I just realized that with close to 50,000 miles I may need to purchase the ESA in the next 30-45 days. Am I correct that I must get it within 30 days of hitting 50,000 miles even though I am only in year 3? If so, how would Tesla know when I hit 50,000 miles? Finally, is the general consensus that the ESA is worth it especially since I plan on keeping the care for many more years?