I have a 2003 Passat B5 which has a slow leak of the coolant, I need to add around 500 ml of coolant every two weeks. The pink coolant is getting expensive to replenish, so I am thinking about just using the distilled water. The car is otherwise running fine, but still, I don't think it is worthwhile to find a shop to fix the leak for such an old car. What do you guys think? any opinion or suggestions?