Help with finding motor that will pull a toy train

I know you have all this great information explaining about motors, volts and torque etc. but it all that techinical stuff makes my brain freeze. All I want to know is what 6 volt motor will make my 1988 vintage Playsckool train run again. I have tried three different motors and none are able to pull the 4 plastic cars around the track. I’ve tried high torque but do I need low torque?
The train runs on 4, 1.5 © batteries, the shaft of the old motor is 2mm, (a worm gear fits on the shaft, which turns the front wheels) the motor measures around 22mm wide by 33mm long

Does anyone have any advise on the right motor ?

If there is a specific motor already used, can you post a photo of it? Finding a motor which is a drop-in replacement is not easily done.
If the motor you tried is not sufficiently “powerful” to move the engine and the cars, then you need higher torque.
We have never sold this product, don’t have it here so don’t know what the stock motor specs are.