The mobility kit has tire goo (similar to Fix-a-Flat) that will temporarily plug holes, and allow you to get to a shop to have the tire fixed. (Of course, it makes a bit mess inside the tire, too...) That goo expires, and needs to be replaced. Here's a thread about it, including a video of how to replace it yourself with Slime. https://www.macheforum.com/site/threads/tire-mobility-kit-question.22247/#post-676767