Here is the secret to how to get grease into the hinges.
With the steel tube welded in place, a void surrounds the hinge pin between the two bushings. All you have to do is drill a hole through the hinge pin so the grease can get to the center of the pin. Note the small hole in the side of the hinge pin. That is where the grease gets into the void. Applying additional pressure on the grease with the grease gun's pump action forces the grease out into the bushings. There is no other way to grease a hinge bushing and actually get the grease inside the bushing where it will do some good.