2004 Vauxhall Corsa leak in driver side footwell

There's a couple of rubber vents that block up with leaves and the like
I usually clear both by removing the wiper arms and then the black plastic windscreen black plastic scuttle.
the vents are at the lowest points through the firewall easy to spot and clear.
And while your at it it's a good idea to really douse the wiper spindles with WD40 as they're prone to corrosion.

I had the same problem and yours is most likely the same.If you look behind the servo you will see a plate with a gasget around it which the servo is attached to, and its this gasket that goes.I just got a paintbrush and roofing fix that i bought from screwfix,I painted this all over the gasget all the bolts around that area and the car has just about dried out now.It cost about £14 for the waterproof sealant and as it was cheap,I made sure that I put it on thick.Didn't take long either and as said job done