Finding a lubricant that is designed just for your machine can be difficult. Most commercially available lubricants for treadmills are composed of food grade liquid silicone which has as much in common with spray silicones as a fish has with a bicycle. Other treadmill lubricants use a synthetic polymer and others use products such as Teflon or something as simple as wax. The key is to make sure you use a product that is designed to work with your treadmill and has been designed to work exclusively with treadmills.
Another important point is to make sure to keep the top of the belt clean. Dirt can have its own insulating effect on the walking belt. What we suggest is buy a new pair of shoes for each person that will be using the treadmill and only use them when walking on the treadmill. This keeps dirt, road grime, sand, etc. off the top of the belt. It is surprising just how much trash can build up on a belt just from people carrying dirt on to it from their shoes. We also suggest cleaning the top of the walking belt at least once a quarter. It is easy to do and any treadmill belt cleaner along with a clean nylon bristle brush works great to keep the belt clean and running at as low a temperature as possible.
Many people don't realize the need to maintain the most important part of their treadmill. The dealers are sometimes only concerned with making the sale and getting the product out the door. Maintenance will always be a necessary part of using your treadmill and the belt is the most important part to maintain. If you maintain your belt well and keep it properly lubricated it will not only make your belt last longer, but also keep your treadmill running better for longer. It is relatively low effort and considerably cheaper than the alternative, in short, it just makes sense. So keep up with your maintenance otherwise you could have much bigger problems than you expect.