I had to file the front sight on my GPR, and honestly, I still need to file some more, because it hits dead on now at 50 yards, but the rear sight is still all the way up. I need to get it down so the rear sight is somewhere in the middle.
They make the front blade too high on these guns and expect them to be filed... not sure why, but I've talked to a LOT of GPR folks who had to file theirs. It's just part of owning one.
I touched mine up with BC Perma Blue and a Q-tip, just like Musketman suggested. Honestly, I found that the sight is so hard, that filing wasn't cutting it nearly fast enough, and ended up taking a grinding wheel to it. It still came off so slowly that it wasn't a problem... you just gotta be a bit more careful. Mine was shooting 6-8" low, which is quite a bit more than yours is, so I had a bit more metal to remove as well...
Good luck, just take it slow and easy, and shoot it a lot between filings. Like was said earlier, metal won't grow back.