I am often banging on about the rubbish products out there on the market but there is a beacon of hope. Metabo. Mmmmm… Lovely German made products. They cost up to four times as much as equivalents but they seem to be reliable and they are a joy to fix. Windings are all nicely sealed, brushes designed to protect the commutator, wires are nicely routed and secured, construction that is simple for ease of servicing, and parts are that readily available.
We do a bit of work for a company that gives their angle grinders a real hard workout. Usually it is only the switch or brushes or power cord that fails but I did have one recently that had a stuffed armature and field coil. To be fair, and they do put in protection against it, what may have happened is that a stray metal fragment probably got caught up inside the angle grinder. Anyway, the field coil was not to badly priced but the armature was expensive. The repairs would have cost about two thirds of the cost of a new one.
I have not checked out how the switches actually fail but they have rubber seals all over them to keep out dust. I was not to keen on the push-in method of connecting solder covered wires to it. Solder and connections is often a bad match but in this case it seem to be reliable.