Q: Leaky thermostat

It should be leakproof with the supplied gasket used alone. If it is leaking the flanges might have had residue on them, be distorted, or pitted. Although adding sealant "might" overcome those latter defects when you disassemble it just be wary of their being an underlying problem because the supplied gasket alone should have been sufficient to create a seal. Also, the torque on the bolts has to be even and to specification. If out of spec, it will leak. If the leak is REALLY small, that is less than a drop per minute, you could probably get away with driving it for SHORT distances if you can’t avoid it. Obviously, fix as soon as possible. If you desire that the leak be repaired by a certified Mechanic, dispatched by YourMechanic right to your location, please request thermostat housing leak repair and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.