The great things about oil-based clay are that it has a pretty long shelf life. If you keep it sealed, it should last for several years at most, but even if it’s opened, it should last a while since it doesn’t dry out. If you find that the oil-based clay isn’t soft enough, there’s a solution. Since the flexibility of oil modeling clay relies on heat, you can use a hairdryer or an oven to warm up the clay, which will make it softer and more pliable.
You can take a look: What Is Oil Based Modeling Clay?