Not sure what expansion tank your car has , but I would bet that the fluid has never been replaced . On my own 2006 car the fluid smelt burnt and was black and very thin (should be green on mine , possibly red on yours ...an Important detail ) and no history of it ever being replaced.. My system takes just on a litre to replace and the expansion tank is a throw away servive item as the filter is built into the tank.
The service kit looks a bit like this depending on model. Just have a look somewhere above the PS pump for a tank like the one shown here.