I have been using Envirosafe for well over a decade, mostly in old Fords without changing anything in the system. In 2007 I was driving my newly acquired 2001 PSD home when an adjacent hose clamp finished wearing a hole in a steel AC line. I brazed the hole and charged with Envirosafe. That worked fine. Recently the compressor failed. I replaced it and again charged with Envirosafe. It has been stated that Envirosafe is propane plus butane. Anyone know the ratio? It seems to still be expensive considering that the components are a few dollars a gallon. But it is in a handy container, it works, the cost per system is small, so I will keep using it. I recently bought two 30#. But, the only thing I have used for leak testing a newly assembled system is air. What about using propane for testing? It should be a more realistic test, will activate a gas sniffer, is easier to get and a lot less cost than Envirosafe when it leaks out.