That's what I was trying to think of!! ACETONE, always works for me.
I used to but old surplus military guns from CMP, etc. Most were always very oil soaked.
I would lay them in the hot sun on black plastic and the oil would just run out of them. Like old wood school floore, if anyone has experienced those on hot days in school?
Then I'd brush on the acetone over and over in an old cake pan until it was really dirty and full of oil.
Then clean acetone and start over, over and over until happy.
Never actually immersed and soaked in acetone, probably would work best.