Some 5 or so years ago, I replaced my condenser with a new one, having identified a leak around the lower mounting point on the supercharger side of the engine bay. At the time I remember reading of the risk of poor mounting rubbers precipitating the failure of condensers, and I replaced all of mine, top and bottom.
Fast forward to the present, and as I shine my ultra violet torch down to the base of the condenser, I see almost symmetrical fluorescent glows from each of the lower mounting points. Needless to say, all refrigerant is long gone.
On removing the condenser, the rubber bushes are still intact and in place, and there is no sign of damage or trauma apart from the fluorescent dye which has leaked out. No work had been carried out anywhere near the condenser since it was installed.
I have ordered a new condenser and receiver drier, but am wondering if I need to do anything differently this time?

 

Is there any signs of rubbing at all? Can you tell the source of the leak? Is it just an O ring at the joint, failure of the metal, or a crack?
I've had two X300's, one was a very neglected XJR and both had excellent AC with their original condensers.

What I do for AC work is I have a gas detector for hydrocarbons that is good down to 5 ppm. When I am looking for a leak I evacuate the system ( if possible) and then add between 5-10 psi of propane from my BBQ bottle. Then I run the gas detector around all the joints and I can usually find a leak very quickly.

 

Herewith photographs of the leaks under ultra violet light. Seems to come from the mounts, and be almost perfectly symmetrical

 

Definitely looks like it has cracked at the mounts!

 

That does indeed look like the mounts are not doing their job.

Can I ask if you've made sure that the condenser was properly sandwiched? That top metal plate also allows for some rubber to peek through the holes before its tightened down with a nut. If there isn't some compression keeping that condenser sandwiched, then it could be allowed to move when driving over potholes, speed bumps, etc.

It's really the only thing I can think that would create this problem for you.