I recently developed a slow leak in a tire and made the stupid mistake of filling it with Fix-a-Flat. (don't do it, people!) After realizing the huge mistake that I made, I called them up and asked what they could do. They had to clean out the fluid that I added, find the leak, patch it and check the balance. They knocked it out in under a half hour and charged me for the standard tire patch. It's been two weeks and no leak.