Rust in crumpy Hilux footwell/ rain leaks in

[BlakeNZ]

Hi, has anyone had any direct experience with the cause of rusty footwells in a hilux (mid eighties)? I was looking at a LN65 and the previous owner said that the the rain came in the scuttle panel (vents in front of the windscreen) and pooled in the footwells(with obvious results.)
Obviously there must be some rust holes out of sight there somewhere. The windscreen looks well sealed, and the firewall still appears to be in good nick.
Is it a interior/dash out job to find (and SOLVE) the issue, or will removal of the scuttle panel give enough access?
I had the suspicion that the cost of repair could blow out , so I have walked away from the vehicle, but would like to know for future reference. Thanks for any input.

[Bruce Balis]

It all starts in the gutter infront of the windscreen, leaves/mud falls through the slots in the pannel and build up in the 's' bend in behind the front gards, that in turn holds water and rusts out,flowing inside and rusting the floor and usually taking the firewall corners with it, if youre ever in there cut the 's' bend out to allow the crap to flow straight out, Valvoline do an awesome product called 'TECTYL' go nuts with that afterwars and thatl make it last another 32 years

[Bruce Balis]

heres some terrible photos, one side of the truck shows the origonal small opening and the other (if you squint) you can see ive cut ithe opening bigger, and anything i cut out and replace i use 16Ga zintec, i hate rust....but love old toyotas