I can't remember the last time I bought a replacement air element. I just take them out and give them a
tap on a hard surface and put them back.
Only if it's obviously caked in dirt it warped/ damaged do I replace them. I have done fine this way for over thirty years. I even read ibn an article on basic mower maintenance to do this, in the 1980s.
I have never worried about replacing the foam donut at the bottom, as the filters I have used, locate tightly in place anyway, and the filter housing cap ensures it can't come off. If one fits looser than you'd like, you could try placing a piece of foam under the rear cap to hold it in position.
