I had this Einhell BT-AG 850 125mm angle grinder a few years now. I have it mounted on an angle grinder cut off base and I use it only to cut metal pipes, rods and screws.
After a lot of use I had to change the armature bearings so I took everything out, I replaced the bearings and I added new grease in the gearbox.
Bearings I used:
Front Armature Bearing: SKF 629-2RSH
Rear Armature Bearing: SKF 627-2RSH
Main Spindle Bearing: SKF 6000-2RSH