The camshafts are hollow for oil to pass through them. There is a press fit plug in the rear of the camshaft to seal the oil in the cam. Sometimes the plug comes loose and oil pressure bleeds out of the rear of the camshaft. With your compression getting worse front to rear it seems logical that the pressure loss could be collapsing the lifters, with the worst ones being closest to where the oil pressure is being lost. Ie, #8 has the lowest compression and is closest to the suspected missing plug.