my clutch MC went out a few years ago and leaked fluid onto the carpet inside the cab.
it left a small stain directly below the push rod, i changed it immediately after i saw it.
unless the carpet has been changed you should see signs on the carpet under clutch or brake MC's if it was leaking.
looking at the pictures, it looks like some bubbling on the insulation around the gas pedal area(heat?)but no evidence of clutch/brake fluid stain.

 

Just checked Master cylinder closer and it's not an Aisin.
Looks aftermarket and also looks like they re-used reservoir.
I'am just going to insulate and replace carpet and move on.
Thanks again for all the input.

 

Cool. Actually looks pretty clean. Just make sure your exhaust is OK before you proceed with any work. Happy new year.

 

my truck has the same thing going on in the same spot... but it doesnt look the same it almost looks like its just wearing away but i have a carpet and a rubber mat down on it so idk

 

So, are you going to pull back carpet and see what's going on?
Check for leaks or signs of previous leaks.
I have new carpet, just not a priority to install right now.
Also will be installing high temp sound deaden'er (dyno-mat)