Brother Genuine High Yield Toner Cartridge

Purchased in 2013. Problem started as printing numerous fine black vertical lines "streaks" on my print-outs. According to the printer self-test, I have only used about 40 percent of the toner, or 4233 pages. The drum diagnostics show it is only 10% used-up. Cleaning corona wire didn't help, nor did cleaning the drum roller or scanner window. The problem is on the roller of the toner cartridge, which is "grooved" like a vinyl record , the grooves correspond to the lines on the paper. Indeed, on the end of the roller the problem is worse, where the roller has been heavily "eaten" into, and correspondingly, there are gobs of toner in that area, I assume because of the resulting gap. Unless some hard-shelled bugs have penetrated the inside of the toner and wedged themselves against the developer roller, my suspicion is that this toner cartridge is defective. Should I be entitled to a replacement, free, or at a pro-rated cost? I am tempted to risk making a mess by opening up the toner cartridge to see what might be "eating" at the roller. It is weird that the problem just came suddenly. The problem has the appearance of multiple hard objects rubbing against the roller. I'll have to replace the toner cartridge and hope that by air cleaning and cleaning the drum according to the manufacurer's directions, I can continue to use this printer. Does anyone know what causes this damage? I tried to find some information with a Google search, but could not. I emailed Brother Customer service and received a reply, but the e-mail was "blank". An update a week later: I did get a reply from Brother, using their website e-mail customer service, but for some reason their email showed as "blank" until I clicked it to respond to it. Anyway, after sending them the model number of the printer, a picture and description of the problem, and a print-out of the printer self-diagnostic report, they sent me a new 750 cartridge which arrived expeditiously. The one star rating is based on the quality of the cartridge I bought, but if there were a star rating for customer service on a defective item, they would get 5 stars for solving this problem satisfactorily for me. Hopefully, the replacement cartridge lives our all its allotted days. As a postscript, I disassembled the defective toner cartridge (having to destroy it in the process, not wanting to take extra time to do it otherwise), and discovered the problem was spots of dry, hardened, accumulated toner on the very thin flexible strip that massages the toner roller on the bottom. I was able to remove the spots, but it took my fingernail to do it. Being able to restore it at this point doing that would be little use at this point, since the foam on the roller was already damaged. The toner is a very soft material, but caked on the metal strip like this, it would be sufficient hard to abrade the foam on the roller, as it did. Before installing the replacement toner cartridge, I did blow out the printer and drum area with compressed air, and wiped the drum roller with a soft cloth and strong rubbing alcohol, in agreement with Brother's instructions.