black streaks when printing on 3100cn

Soon (a few hundred sheets) but not immediately after replacing black toner cartridge, I started getting several dark streaks the length of each page, between the middle and right edge.  I tried replacing the toner cartridge in the hopes it might just be a defective cartridge that was somehow leaking, but that didn't seem to have any impact.

I have cleaned everything I can see and reach without taking apart the printer, though perhaps I missed something.  I removed the drum and found streaks of black toner on the blue film.  I have wiped off that toner from the blue film (and advanced the film to get all of the toner), but when the drum is put back into the printer and the printer gets ready to print, even before printing anything else, stripes of toner are redeposited on the blue film.  Most of the streaks are around 1/2 wide; several are close together and there are larger gaps between others.  The stripes seem to get darker the more pages I print.

Any ideas about what could be causing this and/or how I might fix it?  Thanks for any insight you can provide.