you have to make sure you are putting on the exact same slider. A lot of them LOOK the same but there are minute differences that will cause your zipper to fail again if you don't put the correct one back on. For r coil tent zippers there are S ,C, and CN type #5 sliders, and there are also different sizes. #5 is most common but there are some out there that use #4.5. Your off and el cheapo brand sliders won't be marked.

Most of the zipper repair kits do not have the full spread of different kinds of sliders. You need to look at the slider carefully for the code number, usually on the "nose" of the slider, and get the correct replacement from someplace like Outdoors Wilderness, Seattle Fabrics or Rockywoods.
tips for making gear