[rovertone]

The condensor is the first thing that comes to mind especially if your s is original. I'm surprised F1 didn't do a vacuum test to check for leaks before regassing. Might pay to query this with them first or find a motor aircon specialist who could do this and trace the leak for you. If its condenser failure its bumper off job to fix which should be straightforward enough for decent independent garage or aircon man. Rough cost of unit itself £100, I bought mine a while back from Jules together with O rings etc. My first port of call would be F1.