You might want to try sudsy ammonia first. Use it with a soft bristled brush (I use a baby toothbrush.... I figure they make them soft enough for a baby's gums, so they shouldn't hurt a blade). Then rinse off the ammonia with water (or a clean rag that is wet... just be sure to get the ammonia off). Finally, make sure you dry the blade with a soft cloth. If it's dried oil, I think this will take a good bit off.

Good luck!