Wow, impressive results. Looks promising. That black line is simply caked on toner the blade can't fully scrape off. Try opening the large door on the bottom of the cartridge, and turning the drum until you see it, then gently wipe it off. Do this in a low light area.
If for some reason it starts ghosting, and you don't feel comfortable replacing the blade, I just got a new toner cartridge in today that I could replace the blade on for you. Also, if you wanted to ever sell those pliers, let me know (Or let me know if they work!).