I have a 2016 Model X 90D with only 40K miles on it. I am reading a lot about MCU1 issues and have been told not to worry until at least 50-60K miles. Are there issues that start to show you many be having MCU1 problems, or does the thing just die? I did purchase the 4 year extended Tesla warranty recently, and if I had or needed to have the MCU1 unit replaced, will it be covered under my extended warranty? What things should I be "keeping an eye on"? Thanks.