Where can I find a copy of instructions for the 3927 Track Cleaning Car
Use either Lionel or LifeLike track cleaning fluid. Replacement sponges (part #3927-25A) and wipers (part # 3927-50) are available from online parts dealers. Pull the car behind a locomotive with the sponge rotating and the wiper carriage down. The sponge assembly snaps into place into the motor drive gear. Here is a page from the service manual.
Larry