Terrible design and botched maintenence. The pollen filter lives in the vent well in the bulkhead, but is inaccessible. The vent well drains can get blocked, the pollen filter waterproof cover can get damaged, or the whole thing can get misfitted after the pollen filter is replaced when the garagehand finds he can't do it in the time he is allowed. Any of these allow rainwater into the car straight through the pollen filter. Same on Golfs, Leons and A3s, but the design was improved on Polos, Ibizas and Fabias where the filter can be removed and replaced from inside the passenger compartment.