Samsung CLP 300 streaking

I purchased a Samsung CLP 300 5 months ago. Initially, no problems at all,
excellent printing. After several months, I noticed streaking and fading
down the length of the paper when I printed b/w. I changed the b/w toner
cart and things improved. Now it is happening again and my cart is around
90% full. Does anyone have any ideas what the problem might be? I have
cleaned the imaging drum and anything else I can see.

Tel