Well, that was instructive.
1, they are not difficult to take apart.
2, the largest piece of debris was a flake of paint (thst probably fell in when I opened it).
3, there is no perceivable wear , it's like new inside.
4, they are fiddly f####rs to put back together!
Still , I have fixed the leak
And decided the click is the motor coupling, which I may have to change along with the motor, as it lacks starting torque for the highest speeds.