This is a long detailed way to clean that fan, if you can get a few chips out into a small glass pill bottle or similar you can try some solvents without spraying them into the machine. I have been very successful with Purell sanitizer but if the recommended cleaner does not dissolve it you might need a small scraper to pull pieces of crud out.
Fortunately you have the newer back grill making it easier to reach the fan blades.
you might need a small scraper to pull pieces of crud out.