It sounds like a farm tractor. I found a large chunk of dust today and I cleaned it with a toothpick. I regularly blow dust out but this was stuck, so I guess the fan i ruined now.
I have opened it up but it seems like a maze reaching it this way. From the outside it's both plastic and thin stripes of metal right in the center where you apply the oil.
I use this machine for my daily work.
Here's how you remove the fan:
It does not require oil - in fact, if you oiled it an any point, it should be replaced and the system thoroughly cleaned of all dust AND oil residue.
If the fan isn't turning easily, replace it.