No pics. Semi circular raised 'indentions' about the radius of the piston, but offset in the bore where it would be impossible to be a piston that runs into the valve seats on cyl 3. Same patter between 2/3.
Head guy has been doing it 25 years and said he has maybe seen it once before. No idea on cause.
The return side is low pressure ! The only time you can have a miss is on high pressure side lift pump to I/P ,I/P to injector or air in the system,bad injector,or injuction pump . If your injector is leaking than yes you can have a miss only if it's on the pressure side !