A common source of a coolant leak on the WK2 Diesel engine is from the EGR Cooler O rings and mounting cups.
On First inspection this appears to be from the cooler unit itself but in majority of cases the cooler is ok and the leak is from some mounting cups and some O rings and sit below the cooler.
In this short video we have a cooler off the vehicle and talk you through the parts needed and where they sit in the engine.