It sounds like it's well past "going" bad... like the printer is basically toast. I have no experience refilling toner cartrdiges, but I did ruin my last Brother printer by trying to push an (OEM) cartridge too far past its nominal end-of-life after taping over the window in the cartridge that normally allows the printer to sense the toner level and stop working at whatever defined point they do until the toner was replaced. When I say "too far", I mean I continued to use it after it first started only lightly streaking the very occasional page, but basically still printed text well enough for my needs if I removed the cartridge and gave it a good shake on an increasingly frequent basis, to the point where I had to do it every time I printed something. (In retrospect it was a foolish assumption, but I was figuring that the printing would just get lighter and lighter until it was no longer usable, rather than doing something that might damage the printer itself.) But then at some point, for no readily apparent reason, the streaks suddenly became constant and dark. I had a spare printer with compatible replaceables still sitting in its box, so first I tried the new toner and then the new drum, but whatever had become dirty or damaged seemed pretty clearly to be in the base itself.
I briefly tried to take a look into its guts (without actually "taking it apart") but couldn't figure out what had happened, and since I had a spare (and the printers are cheap, on sale) I just tossed it and started using the new printer. Further evidence that the problem was in the base was that I used the old drum (which hadn't reached its nominal end of life) in the new printer for a while and it worked fine, so obviously hadn't been the cause of the streaking in the old one.
To make a long story short, the moral of the story afaiwc was that if you're going to screw around with printers in ways they're really not designed to be used, you take your chances on catastrophic failure. Presumably you saved more than the price of a new machine (on sale) by refilling your cartridge so many times, so I'd just consider it a lesson learned and going forward, either refill cartridges only once or maybe twice, or just start using "new" generic cartridges every time. Personally, I ended up staying with OEM, but then I really don't print at home much at all these days, so the cost isn't a major factor, more important is my lack of desire to find space for a permanent "spare" or to even think about maybe having to replace the printer (again) on an "emergency" basis when they might not be on sale...