Not a huge surprise to this group, I know. My Coupe was redone in the early '80s. Really proper, professional job. Early this year, my Coupe was running well, I was happy with the Webers, replaced the rear suspension bushings, all was good. But then I looked at the rockers that I had to use to support the car while I took apart the rear suspension to install those large and decayed original rubber mounts. Everything looked fine. I even removed the outer rockers, hey, not bad! Then I removed the carpets and all those layers of padding/insulation and decayed '70's carpet underlayment. I found corrosion in the passenger footwell, at the inner sill. 
After therapy, I removed the rest of the carpets and was saddened to see rust under the seat platforms. Man, what a sight! Quickly made a plea to my favourite restorer and a couple months later he had a spot, cut those seat platforms out, ground the entire floor to shiny metal, prepared and Por-15 and topcoat with fresh Baikal Blue. Looks like new. If you are feeling lucky, have a peek under the seats of your Coupe. There are 2 large openings that will reveal what is going on in there. But don't do this alone! Anyway, I am happy I caught this before this really took hold. That outer/intermediate/inner sill video Markos filmed still gives me nightmares!
After therapy, I removed the rest of the carpets and was saddened to see rust under the seat platforms. Man, what a sight! Quickly made a plea to my favourite restorer and a couple months later he had a spot, cut those seat platforms out, ground the entire floor to shiny metal, prepared and Por-15 and topcoat with fresh Baikal Blue. Looks like new. If you are feeling lucky, have a peek under the seats of your Coupe. There are 2 large openings that will reveal what is going on in there. But don't do this alone! Anyway, I am happy I caught this before this really took hold. That outer/intermediate/inner sill video Markos filmed still gives me nightmares!