Away from home, acquired 3081 Marklin diesel locomotive.
When connected to 15V the motor runs, lights are on, but then it emits a squeaking sound. The sound disappears when the rotor axle is gently pressed with the tip of the finger.
Also, copper mesh is totally worn and reduced to less than half its size.
As said, being away from home, cannot change the brushes, and cannot lubricate.

Guessing the cogwheels are not damaged because the motor runs perfectly and squeaking sound is NOT constant. Damaged cogwheels would emit the sound all the time.
I understand it`s difficult to diagnose the issue based on my data, but still, can you suggest whether the abnormal sound can originate from badly worn brushes which leads to increased pressure on the rotor by brush springs. Or it needs a drop of oil.
All said, it is a mystery to me how the abnormal sound completely disappears when the axle is pressed gently towards the brushes. Any ideas are appreciated.
Thank you.