Got my 25 re-gassed the other day. The guy just connected it in to a machine for around half an hour. The machine ran through a sequence of vacuum testing the system, and refilling, if found ok (with a bit of dye to give away any leaks that could develop). He said on average around 15% of gas is lost per year, or more of the system is damaged. I was told the gas we currently use is going to be illegal from 2022, as the new a/c gasses are alot less of an impact on the environment. Me, I do regularly exercise my cars a/c in the winter. Makes sense to me to exercise the seals