indeed, that's a usual problem with all cameras, not only with FEDs. The sanding is too harsh a method, of course - it's likely to cause more problems, I think. I always cured the scratching by removing a pressure plate (that's not difficult at all), and polishing it on a piece of rough leather with some very fine polishing paste on it (we call this paste GOI, and it's green because the abrasive there is chromium oxide). Some kind of such fine polishing paste should be indeed available in your place. Just take a pressure plate and polish it well, as well as the whole film path in your FED - I assure you, the scratches would be gone.
Cheers from Moscow,