A close friend of mine has found a correct size commercially available worm and gear to replace the worm and gear in a Wagner designed power truck. If you have a noisy Wagner designed power truck changing the worm and gear will greatly reduce the noise.
An article on how to install the commercially available worm and gear into the Wagner gear box should be published, I hope, in a future issue of "O Scale Resource" emagazine http://oscaleresource.com/
This is an important event. Many modelers have tried in vain to reduce the noise of their power trucks. No more information is available. The fella who discovered the worm and gear plus how to do the conversion will author the article. He richly deserves all the credit.