Re: leaky XY?
You willhave a hole in the plenum chamber near the RH footwell vent. To see exactly where, crawl underneath dash (helps if you are small!), and remove vent, then check area with a torch. If you can't see anything, get a mate to trickle water into your scuttle panel while you look.
Unfortunately, not easy to fix properly! You will probably need to cut away the upper cover for the plenum, put new metal in, then reweld it. Not a job for the faint hearted!