Yep, de-silvering... Won't affect images but will steadily get worse with time.
The bad news - it's not really repairable. If you're invested in the camera, finding a donor body and swapping the prisms is probably your best option. Luckily there are lots of K1000's in the world. As others have mentioned, I would send it to Erik Hendrickson and have him do a full CLA at the same time.
The good news - it's not a Leica
I had to get the rangefinder prism in my M2 re-silvered. You do
not want to know how much that cost...