Where is the radiator cap?

First: Don't add a "head gasket sealing" product! This can cause more problems than it will ever solve. Not to mention, the theory that you can seal a head gasket without removing the cylinder head, inspecting the head and block surface, refinishing as needed, and reinstalling with a new gasket and new bolts is unfortunately not accurate. Beyond that, what if you don't have a head gasket problem? The "radiator cap", however, would be a coolant reservoir cap on this vehicle.

I agree! Additionally - there is no such miracle in a can product that will repair a failed head gasket which includes the ‘guaranteed to work’ Blue Devil - over the years I’ve tried them all following the manufactures instructions to a T.. Some actually did stop the leak - for a very short while - then vehicle had to be towed back to shop for the required mechanical repair - which was then hampered by the residual product left behind. Save the money to put towards the necessary repair. Good luck!