I have a very slight head gasket leak. One mechanic has suggested, as a first step, to re-torque the head bolts and then apply to the leak area a high-temperature silicone sealant. I saw one sealant advertised as being impervious to oil, and which will withstand temperatures to 400 degrees F. Other than the small leak, there's no reason to pull the heads, etc. The leak is only to the outside of the engine block. There's no mixing of oil and coolant.
Has anyone tried these sealants? The mechanic believed this would most probably fix the leak.