My not official way of cleaning the head fan is to attach an old C-pap hose to my shop-vac and put the rubber end in the outlet of that head fan, With the Glowforge completely off the shop-vac is turned on and if gunked up enough will not even turn the fan. I then pump in the Alcohol Hand Sanitizer that is very good at dissolving gunk and the sanitizer and dissolved gunk are sucked away by the shop-vac and I add more till the fan is spinning nicely and the gunk is dissolves away.
I then let the shop-vac run spinning the fan for a half hour or more so there is no possibility of any sanitizer about, and for some time to come the gunk supply will not slow the fan.