Well Nick, if Metal Matrix "Composite" is not a composite material, then what is? For once, the public copy of the regulation shows the same information as the working copy in this case:

https://www.fia.com/file/61689/downl...token=hVJqMBK-

The use of composite is allowed for the following parts:
 Timing cover
 Air filter box
 Air ducts for cooling (cockpit and boot (FR) / radiators / intercooler / engine auxiliaries / brakes)
 Homologated exterior bodywork parts (see article 902)
 Windscreen lower trim
 Door trims (FR)
 Dashboard (FR)
 Seats
 Supports and fixings fitted inside the cockpit (except seat brackets) and inside the rear boot
 Protection covers fitted inside cockpit and inside rear boot (FR)
 Foot rest for driver and codriver (FR)
 Console / support for switches…
 Steering wheel
 Heat shields
 Protections of the bodywork parts (side, floor, inner wheel arch)
 Leakproof box for fuel tank (see article 401) (FR)
 Underbody protections (see article 902)
 Mountings for front and rear bumpers
 Headlight units and tail light units
 Additional headlights housings (see article 503)
 Paddles for power assisted gearshift control
 Supports and fixings fitted inside the engine compartment (except engine / transmission supports)
 Discs for differentials
 Baffles fiited inside engine oil sump and transmission housing
 Fuel tank internals
 Engine parts: see HOMOLOGATION REGULATIONS FOR 1.6 TURBO ENGINES
 Electric connecting box
All composite material parts fitted directly on the engine (parts mentioned in Article 3) and the parts fitted in the cockpit or in the boot mentioned above (FR) must be made from fire‐
retardant material (seats and driver / codriver equipment / energy‐absorbing material: see FIA standarts). The external face of the part must have a V0 level of acceptance respecting
the "UL94" US standard (fire‐retardance capability).
Basically, this list precludes any meaningful use of MMC on these cars.

Somewhere in this discussion indeed lies the truth about the finish on the part. What can I say, it's painful to see all three cars go out with the same broken part (whatever the circumstances), and it's not the first time they failed this year...