Hope this is interesting.
When you have trouble, that the AC empties every couple months below could be the root cause.
I had trouble for 3 Years, that AC works only for 6 months or less. After a certain time the cooling fluid was gone.
Finally, after several trials to fix the issue i found the root cause. Unfortunately I have to say, that from my view (I am an automotive engineer working for Continental) it is a design topic!
The MK2 AC low pressure line in the sill is insulated with a foam tube. During operation there is some condensate creation on this line. The condensate can due to the Foam tube not evaporate. This is the reason, that the Aluminum pipe rottens through. In my case it was just at the front end inside the sill, about 6-8" below the fitting to the condensator.
To determine this leakage, I did an overpressure leakage test with N2 and H2 (Hydrogen is easy to detect with the right equipment at an AC Maintainance shop).
The interesting thing is, that Lotus actually offers a service kit to replace the lines in the sill without removing the sill itself (See technical service bulletin 2006/33) - so they know about this topic.