No, not all gas stoves leak benzene. In fact, most modern gas stoves are designed to prevent leaking of this and other harmful chemicals. However, some older models may not have these safety features, so it is important to check before using one. Additionally, even if a stove is new, it is possible for it to develop leaks over time. If you suspect that your gas stove is leaking benzene or any other harmful substance, contact a professional to have it checked and repaired as soon as possible.