Needles cause leak in Corsa

We've had another leak in the Corsa, this time on the driver's side. Quite
a lot of water must have got through into the car floor channels from the bulkhead between the inside and the engine compartment, we think.

I spotted this when parked on Fell Lane which is quite steep so a lot of water had sloshed back and was visible behind the driver's seat in the footwell.

The culprit is almost certainly a bunch of spruce needles etc collecting where they shouldn't do and so water leaking through a seal that is dodgy - in the middle of the pic.  Removing the plate and replacing it with new sealant is a bigger job than I want to do, so I'll try gumming it up. With the needles sluiced out, most water should flow past without thinking about going through the hole.

Then there's all the water to clear, which is under a carpet which looks pretty hard o get up. One site recommends drilling a hole through to drain the water, but that seems a bit too much.