I have a furnace with AC in the basement. I have poor airflow in my top floor vents (furthest from the furnace). and even the room with the cold air return doesn't change temperature very quickly. Meanwhile, the basement and main floor do heat and cool much faster, leading me to believe that my ductwork is leaky. I've examined the ducts, some of which are exposed in the unfinished basement, and many of them have small gaps and holes. Much of the ductwork runs entirely sealed in the walls.
I've heard of Aeroseal, which can seal the gaps throughout the entire system. The process seems simple enough and thorough. Is there anything similar I can do myself to achieve a similar result?