Putting the cartridge back?

Can anyone help, i have a Java mixer cartridge. I have removed and changed the three seals on the cartridge making sure it was clean first and applied a silicon lubricant to the seals. refitted carefully into its clean space. fitted the handle etc and white seal ring. it worked ok for a couple of days, but now have water dripping through the white ring seal just under the handle. Do i need to fit this white ring in any special way?