Leak in Vauxhall Corsa

[Jessy pie]

My son has a 54 plate Vauxhall Corsa 1.2 Twinport. Just recently a leak has developed under the passenger side,under the dash/glove compartment area. It is not a heavy leak, more of a "spraying" of water, and only happens in heavy rain. About 2 months ago we had to work on the light cluser at that side to change a relay and the fuse box was disturbed. Dont know if this is connected to the leak. I have been told that the corsa has drainage holes/channels that can get blocked. Does anyone know anymore info,please.