interior leak!!!

Sorry to take so long to follow up. Here is how I solved the drivers side issue. I cut an access hole used a shop vac and then followed up with rust converter inside the area. I folowed up with a cover plate.
I still have the small interior leak above the heater box location at the upper seam. I have two choices here,one to open the top of the cowl and weld the seam from above which would be very messy or re-apply seam sealer to the bottom of the seam. I just hate to use 'cualking' to create a water tite situation. any other suggestions and what exactly did they use as their seam sealer, or what is the modern day equalivent.
Thanks
Andrew

EC cleanout2.jpg

EC cleanout3.jpg