Ghosting issue on 102

Hi I run a 2001 Speedmaster 102 8color. Yesterday I had a job where in one spot there was no black image on a 4 color job after about 10k sheets the color bar was tracking up the sheet. The water seetings seemed to be ok but I found the etch perfectly in the bridge roller I changed it and it went away. has anyone ever heard of this? Also I run will my varios on. On the console there is a button to turn the intermediate roller on or off i run with it off should it be on and if it should why?