This will split opinions so before I begin
K-Seal and Steel Seal are products which you can add to the coolant system in an attempt to cure a small head gasket failure.
K-Seal state;
When there is
a small crack or hole (less than 0.75mm diameter) in the cooling system, this generates a low pressure area.
* K-Seal® finds the low pressure area and deposits the special ceramic micro-fibre and copper formulation as it flows through the damaged area.
* Within seconds the crack or hole is completely filled with the ceramic micro-fibres and copper and the repair has been made. This seal is further enhanced by heat to form a repair that will last the life of the engine.
Here is a mechanic who has used it many times over the last 20 years who reckons it has it's place.
His method of use is interesting and not the advice given by K-Seal but again he has had success using it this way.
I have used k-Seal previously on a small coolant loss suspected head gasket on a Vauxhall and it worked to cure the problem. The evidence on the web is split pretty even between the it works and it's rubbish. Since most people generally don't come on forums to say yes it's ok but do when things don't go as expected then I think the people who have had success with it probably outnumber them.
Please don't shoot the messenger

just passing through