Hi ,
In your machine , that is a poor K9 glass mirror with the yellow coating .
this kind of mirrors is not good after cleaning , the coating will be broke.
for the mirror , the quality is Silicon >Mo mirror >K9
If you need Mo mirror ,you can buy online in my aliexpress store.
Co2 Laser Reflector - Shop Cheap Co2 Laser Reflector from China Co2 Laser Reflector Suppliers at Shanghai Weihong Electromechanical Technology Co., Ltd. on Aliexpress.com
Best regards