The contact owns a 2006 Scion TC. The contact stated that after performing a vehicle inspection of the engine compartment, he became aware that the coolant reservoir was abnormally low; eventually finding a leak near the rear of the engine. No warning lights were illuminated. The vehicle was taken to an independent mechanic, who diagnosed a failure with the cylinder head bolts resulting in a coolant leak. The vehicle was not repaired. After investigating the failure, the contact related the failure to Technical Service Bulletin: S-SB-0004-11. The manufacturer was notified of the failure but provided no assistance. The failure mileage was 287,000.