Just to make certain we are on the same page,...Your burnisher is a screw-press tool with a ball on the end? No metal removed in the process?
First, I must admit that my success with burnishing isn't 100%, but damba close.
Success depends a great deal upon the condition of the worn seat.
If it has been punched with a drift some time in the past (most of these machines are older than we are, so I'm not pointing blame), or the seat has been widened by lapping, gouged by a cutter, etc., then somehow we must get back to 'zero' before the burnisher can work properly.
Just like a cylinderhead valve, the seat must be narrow to seal completely, and with oil involved, the final finish must have a mill profile that is smaller than an oil molecule. (Thank Gawd they are big!)
I would post a pic of my simple piloted conical stone for a pre-dress, and my home-cooked burnisher as well, but attachments are still a gliche for the forum.
With a little thought you can conjure them for yourself.