Lift it up and remove the bottom plastic tray. I would first just check where its leaking, if its a joint, remove and clean the pipes where they make contact. You should check the pipes for damage where you see its dripping. Ic piping is quite easily accessable from under, no need to take bumper off if its problem with piping. If i remember correctly, the basic mkv gti had no jubilee clips so you might have to replace part of the piping if the connector clips fail. But you should just take a look at whats causing the problem. It should be easy to see because of the oil..