Sodastream does not sell replacement parts. (That's a good reason to consider buying from another company instead). The older Sodastream models used plastic fittings, and it's very common for them to split. You can print your own replacement, or buy one online. But 3D printing does not produce parts that are strong enough to hold up under pressure, so it may only last a short while. It's probably better to pay a little more for a replacement made of brass or aluminum.