My 2009 i10 had it's fourth annual service recently. At the same I asked for the air con to be checked as it didn't seem to be cooling down at all. They reported that the air con had no refrigerant in at all and needed to be completely re-charged. This they did, and then checked for any leaks, but all was apparently OK. The service receptionist didn't seem to think that this was unusual.

I am puzzled as to how a supposedly sealed system could be found to be empty, be re-charged, and then work perfectly well.

I have followed the advice you give on running the air con on a regular basis throughout the year.