As above, drain plugs in plenum chamber and foam seals around pollen filter and ecu housing are common places to go.

It was the seal around the pollen filter housing that went on mine and I ended up with literally a puddle of water in the rear footwell. Unlike Parkus I was lucky and the convenience module was still dry and once I dried out the wiring everything was fine. You wont believe how much water the foam underlay holds!

Use butyl tape or sealant to seal up the leak.