Can a Marx 1666 be geared down?

[Granpa49]

My Marx 1666 does not need to run at full speed. It jumps the track if you do. However, it is a bit old and doesn't like to pull cars at half throttle. If it could be geared down the motor could run faster without the train running faster. I'm using all original parts - transformer, track, locomotive, etc. I was able to clean the track very well. However, the motor is worn. The gear shafts need to be bushed in the side plates and some of the gears show wear. I replaced the brushes and cleaned everything but it is still an old locomotive. Can you buy new stock that will couple with the older cars? This locomotive coupler has the tab bent straight down that goes into a slot in the tender coupling. The rear of the tender car uses the Marx fork style coupler. What are my options?