I have a lot of trouble with vents getting plugged by insects. I usually try to clear most of the mud with a thin hooked wire. Push it in past the obstruction and try to pull the majority of nest/plug out. The particles of remainder may get into the trans but settles to the bottom. Filter catches anything else.. Been doing this for 40+ years.. (before that I ran manual trans)

 

Vent location >> http://www.selectric.org/06main/th400.jpg