Samsung CLX-3160FN Vertical Color Smear

I have magenta smear about an inch wide all the way down the far right side of my page. Only occurs on a color print.
Tried the following:
*Replaced toner
*Replaced Image drum$$ - Seemed to be fine for about a week, then it came back.
*Did 1/2 page test: Pulled out the image drum and can see the toner on the green drum where the smear is being put on the page. Looking inside at the fuser (looks like a sheet of black 'transparency' film) I can see the magenta smear on that ready to be fused to the page.

So... I think the smear is being put on the drum, or it isn't getting 'cleaned off'?

Any suggestions or advice?
Thanks.