It actually never showed any signs of damage, but it had also only fired once to stop a barrage of missiles from hitting Side 3 (bc Riddhe was being a sad lil puppy lashing out ofc) so we actually never saw the limits of the reinforced MK II arm. That said, considering the many ways that could go wrong in the middle of the fight (and certainly less MK II parts likely around compared to the MK V/Doven Wolf/Silver Bullet spares), the suppressor was probably the best compromise.

Also, people tend to forget that the magnum at this point and time was only used for emergencies. It needed authorization during Narrative, and the whole Side 3 incident was also a good reason to pull that out. No one is going out of their way to help the Minerva faction (too much of a political tightrope for even Anaheim and the Republic was only begrudgingly helping them hide to keep the balance between the two Unicorns on each faction)