Water!

[Kudu]

I had the same problem, I cleared the water drains in the plenum, removed the pollen filter housing cleaned out the area and installed the housing with a bit of silicone sealant on the seal, once I had everything back together I ran a bead of silicone sealant between the base of the windshield and the plastic cover. This I did a year ago and no water since. Hope this helps.

[ranton-inc]

Could be your heater core.... check your coolant levels if they are dropping then its probably that.. other wise its your bonnet release catch or something similar..

just watch it becasue your trans computer under the seat.. and that LEak is number one cause for killing them!!! best you park inside untill leak it sorted..!

Guy at work V6 4 Mo B5 Passat Died a horrible death from that exact leak!

[kiwi]

yep the ecu's in the floor well would be a check ASAP!

F-ing B5 Passats!  mine leaked like a bitch.. best thing i did to that car, trade it in. 

[BB]

All VAG cars leak. Its part of their charm.

[slowmo]

mine's doing this now too..... noticed this morning that there is a damp spot right under the glovebox and under the floor mat.