>>Running it all year helps stop the seals drying out and reduces gas loss, maintaining it's efficiency longer.

Have you any proof of that, or is it an urban myth?

I would've thought that running it all the time would make it liable to support bacteria in the wet parts.

Yes, leave it on all the time all through the year.

And I think HJ himself advises this in connection with preventing the seals from drying out etc.

Same here never leave the aircon on, just use it as required, or once a week or so for a couple of minutes just to keep the seals lubricated.

Over the 4.5 years i keep a car, i have never yet had a aircon unit fault.

if you are concerned about bacteria then run the heater at both full hot and full cold for some time.

I actually think running aircon continuously is both unhealthy and wasteful on energy.

My last 4 cars have had aircon / climate, and I leave the aircon OFF unless I need it to cool the interior, or to quickly demist. I do try and run the aircon on full cold once a month or so for 15 / 20 minutes to get the refrigerant circulating.

This is the correct use of A/C , as stated in car handbooks.