Ah.
The Rust Clips - which, together with A Mess Of Butyl - hold in the windscreen on pre-1980s cars - have done what they usually do, again: caused the scuttle panel to corrode and make a horrible mess.
You'll need to remove the windscreen and effect rust repairs.
New Rust Clips are hard to find these days, so IMHO you're best off replacing the windscreen with the late 240 type with the single piece neoprene seal. You won't be able to fit the Mud & Dust Collectors (aka stainless windscreen surround trim) with this new type of seal. You'll also need to plug up the holes in the screen surround where the Rust Clips used to fit.