Not an Audi, but a late 2009 SEAT Ibiza 1.4 SC with a BXW petrol engine, my daughter has owned this car from new, but has been working abroad for 4.5 years so I took it on while she was away, anyway, she is back and I've sold that car back to her at a good price. After a spot of warm/hot weather, I was told that the air con is hissing and needs some gas, well she got the "needs some gas" bit right, on examining it I discovered that the area around the pressure sensor was a bit oily and dirty, sniffing it revealed that it was passing R134a probably through the pressure sensor body, so I bought a new latest version pressure sensor and O-Ring seal and replaced it. While I was at it, I cleaned up any other oily looking areas using Gunk and left things to dry off before sniffing these areas. Initially I found a leak site at the over pressure disc area on the compressor body, so sprayed that area with a cleaner - washed it and gave it a couple of days for any solvents to disappear! Still detecting a leak, so used a leak spray on that area - and discovered that the leak was not at the over pressure disc but at the body gasket near there. That was a better result as at least I would not need to find why the over pressure disc had started to leak. So, it looks very much like I need to get that compressor replaced along with new seals and drier etc. One problem is, I can only find from aftermarket a 120ccm version of that compressor - the one SEAT, VW etc etc fit at factory is a 140ccm version - same body type, I'm thinking that using a smaller compressor will not cause much of a problem in Northern UK temperatures, is this correct. Also, has anyone else seen or heard about these Denso compressors leaking at the body gasket, car is obviously 8 years old, but I've owned 13 year old VWs in the recent past and one of them had a variable displacement Denso compressor that was still okay at 13 years? Edit:- by the way, to date this car has never suffer any collision damage etc, so that leaking would not be the result of being in a crash situation.