Small coolant leaks are the worst to find.
Those V.W electric auxiliary pumps were an addition on later models. I think they realised when the engine turns off and the main mechanical pump stops, they needed to purge stored heat from the engine cyl. head by keeping a small coolant flow and running the fans on a short while.
A coolant leak anywhere is best traced when the engine is hot, idling and the cooling system is pressurised. Once you start driving the car, the airflow around the engine will spray leaking coolant everywhere, making tracing difficult. Any coolant leaking over radiator fins will soon corrode them!
Try removing the engine tray, wipe everywhere clean and look for a leak when the engine has idled to normal temperature. The method used by workshops to confirm a system leak (head gasket, cracked block, water pump seal etc) is to pressurise the system cold at the filler cap to about 12 psi and see if pressure holds for 20-30 minutes. Then repeat with a hot engine.