I respectfully do not hold with such claim regarding the M103 head gasket. I certainly do not believe the head gasket should be changed because of a certain mileage achieved.
The M104 is known for excessive frequency of headgasket replacement necessity. But even those engines do not ALL require this repair. It is easy to get the idea that all engines of a certain model that frequently have a certain failure will require the repair. This is not true. The service people see many failures of a certain model, but that means the failure right is something like 15% which would be a high failure rate, it does not mean that you are guaranteed to experience such a problem. 85% chance of NOT experiencing such failure is not real bad odds.