The information provided is for a 2002 Duffy 18' Classic. Many systems and components are common across models and years.
It is up to you to determine if this information applies to your boat or not.
Our boat has a model BU5-4001 36V DC motor, likely manufactured by Nidec/Tennant/Advance. It has four brushes that require periodic inspection. These are industrial motors designed for far more use than your boat is likely to have experienced, so this is unlikely to be a problem area.
Ensure that it is not possible for the motor to receive power.
Flip open the clip to loosen the metal cage covering the brushes and commutator, then remove it.
The four brushes are now visible.
Reinstall the cage, ensuring that it is clear of electrical terminals.
Eurton Electric in Whittier, CA rebuilts Duffy motors and may be a good source for parts.
D&D Motor Systems in Syracuse, NY offers modern replacements for Duffy motors and motor controllers.