I noticed I was getting marks on the necks of some 30-06 brass I was FLSing. The marks are not deep when I looked at the neck sizing button in the sunlight I can see streaks of brass How do people clean the brass off the inside of their dies and their neck sizing buttons?
The die was second hand die.

I would use some copper eliminator as from Hoppe's. As it take out copper from the barrel, it could also remove copper from your dies. These stuff are pretty safe if used as instructed. You may also use a copper brush after stoftening it with the copper eliminator.

I tried some butch's boreshine which seemed to take about half the deposit away. I did not feel confident to "go in harder" and leave it in longer.
I'll give the Hoppes copper solvent a go.

I have no idea what copper cleaning products are available down under but if you can get some PatchOut your worries are over. No chance of hurting you dies, button OR barrel.

Butches, Shooters Choice, TM, Montana Extreme, Hoppe's etc...most of todays non-ammonia copper cleaning products can be safely left in/on steel as the formulation is designed to chemically combine with the copper/brass and not react with steel...READ THE FINE PRINT FIRST.

Get a Sinclair Int catalog...all the good products are in it.

Chuck the button in a drill motor and POLISH it with 600-1200 wet/dry sandpaper, use Imperial was on a caliber sized brush on the inside of the case neck and outside of the case and you will pretty much eliminate any problems with brass transfer.

Better yet, use FL bushing type dies and get rid of that mangy button and use the nitride coated bushing.

Luck

Get a small piece of a coppper brillo pad and knock that stuff out of there. You will not hurt those hardened steel dies with copper wool.

I had a go with scotch brite scourer and hoppes copper solvent. It worked well.
Thanks for the heads up..