It'll be the upper fan that's not running. It's almost always the upper fan. As H3nry said, lubricating the fan bearing will usually restore it to working order - for a while. There used to be a third party kit to replace the fan with a traditional axial flow unit - much more reliable, quieter, less expensive and better all round.

That "filter block" is actually an ozone filter. If it's so old that it needs cleaning, then it should be thrown out and replaced. I don't recall the recommended interval for replacing it, but it was something like every 50,000 pages or every 100,000 pages. Ozone will give you headaches if the printer is being used in a poorly ventilated area.