The old Amsoil "lifetime" filters were made of foam. They were a pain to clean and what I called dry rot was chunks of foam breaking easily from the rest of the filter.
I am all for saving landfill space, but since I starter recycling long before curbside programs (had to often take different recyclables to different places) I have more than minimized the landfill space I use compared to others. So, for me, cleaning and re-oiling an air filter isn't on my list of things to do - anymore.