MS OEM License breach

"I believe that this only applies to the system builder licenses. The OEM copies sold by Dell will work just fine and legally so with the new mainboard, as it is a 'replacement part' for an existing machine, also provided by the OEM, therefore not breaching the license whatsoever.

If I'm wrong, let me know, but..."

The system builder licenses are OEM licenses. The fact that the OS may work fine does not mean it has not breached the licensing conditions.