looking at all of the forums, this seems to be a common occurrence with Vauxhalls- typically Corsa's. Three areas said to be leaking are the Servo seal, fuse box cover seal and lastly (if you get wet rear footwells) the back light seals.
I have a '53 Vauxhall corsa and have pulled the carpet/rubber up. After pouring water on the windscreen and in the compartment around the windscreen wash bottle, a trickle of water appeared inside the driver compartment. This was above the pedals and from the servo area.
The most common fix found online is to clean, degrease the servo seal (engine compartment side) and then completely cover with sealant..
I'm going to try this tomorrow, but looking on all other forums this seems like the best (quick) fix
Dan
June 2013