wiper cowl vent delete

I just figured out where my leak problem has been coming from too. I have a 73 duster & it has been sitting for about 5 yrs due to lack of funds etc....

On my old dart , it had fresh air vents that you would open manually under the dash. On the duster it had a/c & those areas are not used the same way , BUT the metal is still formed as it would be for those vents.
I.e. , it's rounded indentation , but the actual hole isn't cut out.
Well , that's where my rust is....... :cry:
And i'd like to try and fix it w/o ripping the whole cowl apart at the factory seam or pulling the windshield.
I was thinking of just slicing into the cowl in the area around the wiper blades , just enought to be able to get into there to reapir it & then welding the cutout pieces back in ??
I really just need to get the leak fixed asap(weather permiting) & don't have a garage to rip it apart and do it the right way.

thanks a million ,
I just found this site from a post on moparts , it's awsome !!