May have a partial open path between the number one cylinder and the oil feed passage to the head. This could create both oil consumption and severe blowby. Technically it would not be blowby as cylinder loss would display as higher volume flow of air and combustion products entering the oiling system and pushing stuff out the oil filler hole. Plus lots of exhaust smoke.

I would pull the first and second injectors and inspect for wetness in comparison. Or even turning the engine over with the first injector removed looking for oil spray out the hole.

Other than that is probably general wear but on the other side of the coin head gasket failure in the way I describe is not unknown. It is the way I would approach the problem first anyways.