(4) “Additional” Equipped Parts
Currently there are two Parts that break the usual six-Part limitation: The Knight Core, which allows a second Option, and the Asura Core, which grants two more Arm slots. Since the latter is a Fabled Part, access to it is not guaranteed at any table, but the Knight Core is available to anyone so long as the Knight MEC isn’t specifically disallowed.
Point is, a MEC with one of these Cores can have 7 or 8 Parts equipped, so how are Part Breaks resolved for them?
The Knight Core is easy enough to adjudicate; the second Option Part becomes unavailable when the Core Breaks. No change to the Part Break roll is necessary in this case, though the second Option Part probably shouldn’t also be considered Broken. That is, that second Option remains functional and in inventory for the next open Option slot.
The same approach could be used for the Asura Core, with the second pair of Arms becoming unavailable (but not Broken) when the Core Breaks. This might be a bit punishing, though, so maybe only one of the extra Arms becomes unavailable if the Asura Core would Break? Then if the Asura Core is rolled again for a Part Break, the remaining extra Arm gets an actual Break.
If more of these “additional slot” Parts become available in the future, it might be worth adding a paragraph on how to handle these kinds of Break cases.