GS4 with a grinding noise

[Omaha]

I have an HO scale Bachman GS4 that is about 7 years old, which has run very well until the last time I put it on the track. It now has a grinding noise when running at slow speed. When it is running fast the sound is not noticeable. I do not know if it goes away or is just covered up by the normal noise.

I removed the drive wheel cover plate and lifted the center drive axle so that its gear was not engaged to the rest of the gear assembly. I could still hear the sound at slow speed. This seems to indicate that it is something in the motor or worm gear assembly.

Any suggestions about what to do next?

[ta152h0]

oil the axle ?

[RAM]

Can you oil the worm gear assembly.