VW Golf aircon service/check quandry

[colinstone]

Year: 2001
Make: VW
Model: Golf TDI
Engine Size: 1896cc
Refrigerant Type: R134a
Ambient Temp: 12C
Pressure Low: NK
Pressure High: NK
Country of Origin: United Kingdom
In Aug 2012 a/c system was degassed, vacuum tested and recharged with UV dye and all worked well. By Apr 13 all the gas had run away and low pressure fault was showing on Climatronic self diagnostic.
After a few months away, took car into a/c service centre today for full diagnosis. Due age of car was expecting to find holes somewhere, probably condenser.
System was degassed - not much left - and held vacuum after an hours sucking! Passed vacuum test. Then pressure tested with nitrogen at 10 bar. Passed pressure test. System inspected with UV light and nothing found externally on pipes/joints/compressor etc.
Service centre reckon all is fine but cannot explain why the Aug 12 recharge has disappeared so quickly.
Car currently left with just residual nitrogen while I ponder next move. I am doing cambelt change this week, so thought to replace any a/c components whilst front of car is dismantled.
Any tips on what might be amiss gratefully received.

[install monkey]

gauge connections ??

[charlie patt]

10 bar test overnight if thst holds pressure front seal gone in comp as comp spins gas leaks but must have a overnight hp test first forget vacumn tests they show nothing 2001 golfs suffer from condensors pressure switch and the seal leaking in the test point of the accumulator the only way of noing is a overnight hp test but hurry up if that comp dont work for a while it wont pump very well