Is that rust,iron oxide on that disc?
Mine's worn out,old as, been through hell but never "rusted".I assumed it was stainless steel!
The obvious answer is the one you've assumed but,well,,,, I'd try and reclaim it using care and a bit of emery cloth to see if there are pits under that crud...Would shag out pads.Chances are a Saftey inspecter would fail it,of course but what I'd be concerned with is:Will it crack up on hard use?will it stop the back end from overtaking the front end in the "oh shit"moment?(down hill gravel)Will it sieze up unexpectedly...?I guess funny money would cure those worries,they cost a lot(to me)...good luck.
Eff it,just spotted page three!was on page two...You need new discs!