Help removing finish

[slushee]

I bought an unissued Lee Enfield No4 Brass Buttplate still in its original packing 'grease'.

I have been soaking it in mineral spirits for about 10 mins now, and it almost seems like the 'grease' is more like a graphite coating!!!!!

Whats the best way to remove this?

 

[skirsons]

1870 heavy body paint remover might do it.