Welcome to the Berkshire club. Think there is a total of 3, two on the left and one on right. Have pulled mine a couple of times, heard the air go out but never seen any moisture. Turn you wheels and they are easier to see. As to the computer milage, it's always been a bit off from the old pencil and paper method, ours is about a miles per gallon off, give or take a bit.
2011: 54 days, 2012: 218 days, 2013: 175 days, 2014: 196 days
2015: 188 days, 2016: 72 days, 2017: 185 days: 2018 182 days
2019: 156 days (2009 Berkshire, 390QS, and toad)