WD-40 isn't actually a lubricant so try some some light machine oil.
Better to contact the FF people as they're support is fantastic (pun intended). I once had a problem with the plastic surround melting while my A-frame, years out of warranty, was stored in the Phoenix summer heat. I contacted them about buying replacement parts. They asked what year trailer. When told, they said that was the year they tried another plastic formulation that didn't work out. They sent me all the parts I needed to repair the fan free of charge. Now, THAT'S customer service.
2007 Surveyor SV 230
2013 F150 Ecoboost