Do you have a gen3? There are many areas that can leak, largely on the passenger side, such as the coolant tree, coolant bypass pipes, coolant to turbo pipes and the hose on block between between the engine and the firewall (trunk side of the engine). The hose from the fill up point to the coolant tree can fail as the hose moves on the engine end while staying static on the body. You could try borrowing a coolant pressure tester if you are friendly with a mechanic and see if the pressure reveals anything.
Go to google and type in 'coolant hoses 3sgte' and then go to images, there are loads of pictures with the hoses labelled.