Dell 3100cn streaks on left side

I've had a 3100cn for 2 years and have printed about 25,000 pages. Suddenly I started getting 2 brown streaks about 1/4" wide on the entire left edge of the page. This happens on both color and black & white prints. The more pages printed at a time, the darker and wider these streaks get. I reseated all the cartridges but it didn't help. Is this a drum problem or something else? I took the drum cover off the drum and tried it but I still have the same problem. So the cover must not be causing the problem. I am getting a "Drum Cartridge Replace Soon" message but I thought the drum is supposed to last a lot more than 25,000 prints. Is the streaks a symptom of a drum needing replacement?

 

Thanks,

 

Ed