ChEng

Captain, as to the design of the center bracket, how about making it a solid block. Then drill blind holes in it deep enough and a couple of thousandths larger in diameter than the tube so as to allow the tube to float in and out of the block. Then drill small holes in the ends of the oil distribution tubes to admit oil into the blind holes in the bracket block. This would allow a little lubrication to leak out into the head around the oil distribution tube. The oil would lubricate the tube inside the block, allowing for thermal expansion of the tube and cushioning the tube in the block against vibration. Not sure if this would totally solve the problem, or for how long, but it might be worth a try.