If the brushes are gone and the commutator is burnt, this will blow everything available- Usually the RCD but quite often the fuse itself as the windings get frazzled. It is only the lacquer that insulates them and if this melts they go bang.
Now you know how it comes apart, go one further and check the brushes regularly. Every 500-600 hours of running. It needs to have a record kept of the hours run for a week or so, then you can work out when to check them. When they have worn down they can be replaced and the carbon blown out. If motors like this are looked after they will run for years.
There are videos on youtube showing how to change them.