BMW Repair: 2005 325 ci a/c problems, leak detector, freon

Question
air  condition  continues  to lose  charge..  dealer cannot find leak,.\  can there to an interior  leak?  if  yes  where  should  they look?   please  help.   thanks    chris

Answer
By adding freon in with a dye(use a black light to see)With the dye in the system they would be able to view where it is leaking.Using a leak detector that sniffs for freon works well too.Checking where all the lines attach to each other there must be an o-ring leaking