It's been really cold here this winter (many days under -25C), and this tends to bring out the worst when it comes to tire pressure. Fortunately, I bought my tires from Costco, where they offer free rotation, balance and flat repairs for the life of the tires. All 4 rims were leaking, as well as the valve stems. I'm on year 3 of these tires, and they've been exposed to lots of salts and grime.
Unfortunately, one of the TPMS sensors was a little worn out (original equipment from new) and couldn't be salvaged. They replaced it for $45 plus $15 Labour. I thought this was pretty good, especially considering we usually get hosed on stuff like this up here in Canada.
And now I have good as new non leaking tires, with a fully functioning TPMS system. This system has saved my button several times, allowing me to pull over before the tire gets shredded from being running at too low of a pressure. Yep, I'm a beleiver....
T