fix for TN250 cartridge in an MFC 6800

Anybody have a fix for TN250 cartridge in an MFC 6800.
Same problems with low toner light. Also out of toner caused shutdown. Managed to get it going again by cycling power on and off.
My problems have got worse after using after-market toner cartridges at ~$8 each but I can live with them (save $32 ).
Summary of my problems are
1 Toner shading intermittent. Sometimes gets worse as more copies are done. Sometimes starts bad and improves.
2 There is toner in cart and I would like to get low toner light off.
3 Occasional out of toner shutdown.

I have looked at the TN250, both brother and after-market, and see no window to cover!
Thanks for listening