Before stating the obvious, lets talk about this vent for a moment. Understanding how dryers work will help explain why this roof damper is deterirating from excessive rust.  Dryers bloiw hot air into the drum, which causes water vapors to evaperate, and then it...

This is a pretty straight forward vent cleaning.  It had a semirigid attached with a 90 degree angle at the base of the dryer which is slightly slowing down the air velocity.  We also saw that lint is collecting at the top of the vent, so lint is still able to leave...