I have a couple of old but good machines I've had a quick look at internally. The cpu and gpu fans have hard to remove caked dust on and near the tips of the blades. I need to address that.

In both cases the fan assemblies can be unscrewed to float around on the wire for cleaning independent of the main board etc, but are not easily removed entirely or unplugged.. because laptop design.

I'm thinking CRC Precision Contact Cleaner or a similar product will remove the hard caked dust buildup. Any other product recommendations?