The driver's door is still leaking water onto my new carpet, really gotta get around to doing the seals. As far as I can tell that's the only leak.so - the floor rusted out because there was a LOT of water sitting in it, you can see the 'tide mark' on the carpet going up the side of the driveshaft hump. Most likely it was sitting in there because the cowl has rusted out (just had mine repaired, and it's a fugly job - windscreen out, heater out, wipers out etc) and that's why it's rusted.
A previous owner had slopped body-filler up on the underside of the cowl behind the speedo to try to halt the leaks, and that sort-of worked but it's not a good fix - it depends on how much effort you want to go to and how 'right' you want it afterwards.
But - with that nice repair and lovely carpet, I would be lying on my back and having a look at what's gone wrong in the past so that it doesn't happen again.