Thank you for your question about Casey. I am a veterinarian, and will do my best to help.
Yes, I have seen regularly putting mineral or other oil in the ears of cats with ear mites help. Here is a link about ear mites:
However, are you sure that is Casey's problem? Mostly we see ear mites in kittens, or in adult cats that have been around kittens recently. Most adult cats that come to me for "ear mites' actually have an ear infection
, often a yeast ear infection that can have a dark, crusty discharge like you see with mites. Mineral oil won't help if it is an ear infection, and could make it worse.
I also see black crusty discharge in older cats that have a polyp growing in the ear.
It is always best to get a diagnosis, to know what you are dealing with.
Let me know what else I can help with or answer.