Thanks for your reply. It's a 2008 model and I've had it from new. I noticed (as I learned how it worked) that the compressor would only engage if there was a cooling demand. Basically in FULL AUTO you can only adjust the temperature and in doing so I could hear the compressor clutch cutting in/out. If you adjust any other settings, air direction etc then the FULL part goes and it remains in AUTO. Having said that, one winter coming back from London I was cold and it didn't matter how high I set the temperature I couldn't get warm. It was only while playing about with it I switched off the AIR-CON by the dedicated frost icon button, then the warmth came, so it was basically on cooling away even when set to max. It was a pity I only discovered this at the end of the journey, not the start cos I was cold!..
So, what did the specialist do to the system, well he attached his automated gassing machine, it pressure tested the system fine, because I indicated issues he left it good hour and there was no drop. He then some AC-leak stop stuff, forgotten what make it was but it wasn't cheap, before re-gassing. It lasted 4 days. It's booked in again for this coming Monday but it might help if there was some locations I could point out for them to torch for the dye. I think the pressure of the compressor is pushing it past a leak in the hi side, like the compressor output or the evaporator. The pump is obvious to find but how do you look at the evaporator? getting a bit expensive now, 2 recharges, this magic stuff and a few hours has resulted in 3 weeks cooling. The first time it was recharged it lasted 2 weeks, the second time way less, even with the stop-leak stuff in the system.