You can clean commutator with a fibreglass pen and replace brushes with good quality ones.
I have saved a few using the above method but generally once the commutator has started to get really hot it's life and reliability is reduced i found.
Easy answer is to replace the motor for a hassle free future. Nothing worse than spending a couple of hours working on a machine reconning the motor and it fails a couple of months later down the line, especially if it's a paying customer.
I haven't done a massive amount of work on this model, but if it has an exhaust filter - is that ok ?