napha is, I thought, more flammable than gasoline? OMS is pretty much light kerosene, give or take.
since you ultrasonic'd it in a water solution, I think I'd go with the acetone (because I have a can) or denatured alcohol (safer) soak and agitate to extract any remaining water, then compressed air blast it to get rid of that stuff, then drop it in a can and cover it with some warm oil, leave it overnight to let it thoroughly soak in.