Welcome to the wonderful world of Lionel!
The service manual pages for your Trolley are here.
http://pictures.olsenstoy.com/searchcd31.htm?itm=490
Click on the individual pages, save them to your computer, and print them out.

Following the diagrams, completely disassemble the trolley, and clean all old grease and oil from the motor, wheels, and reversing slide assembly with lighter fluid (naphtha). Clean the motor armature and brushes, the brushplate and gears. Put some hobby grease on the gears, and lightly oil the wheel bearings and armature bearings (both ends). Reassemble, and the Trolley should run like new. As stated above, also clean the track of any dirt and grease, using the naphtha again.

Larry