i've damaged 2 cases of my cr 125, one of them, happened the same as shown, i replaced the case because it opened a crack arround the clutch actuator, the other case only opened a hole trough the stator. i've spent a few hours rebuilding the case the last time that happened, luckily the aluminum parts fell inside the stator case.
i have a home made guide plate with strong screws to avoid that situation. it seems that our 125 don't deal very well with loose chains.
good luck with that!