Magman, i've did exactly the same thing than you on my MBX5T, i've mount the brake servo on the mudguard just next to the steering servo, and i've mount it so close to the steering servo that the gear/arm side of the brake servo can touch the carbon fiber steering servo tray.
So when i apply the brake, the brake servo don't flex/moove at all, because he touch the carbon tray.

No need for carbon or aluminium mudgard.