That's why I know it's low ;) In fact, after picking up some G12, I can even refill it myself!

But why is it low? Is it because the seals in the cap are getting old and slightly out gassing? Or is it because I have a hairline crack in a gasket that's about to be a catastrophic crack?

There's almost two orders of magnitude difference in price between those two repairs!

That’s a very good question. How often is it too low? Once in 2 year? I could live with that. Once a week? Time to visit repair shop.

The lower bound of the leak is a pint over four years. I don't know the upper bound because I don't know the last time the level was ok.