Late to this thread. Really amazed to see that kind of wear. @gunrunnerjohn or anyone else that owns one of these... do these Weaver G2s have a flywheel? I mean a good-sized one that allows a little coasting? Wondering whether the damage could have been caused by a combination of abrupt stops and self-locking gear train. Rubber tires are the enemy. Flywheels are your friend, and back-drivable worm gears are a good thing :-)
Also, thinking that worm wheel is undersized, and it should have been made of bronze, not brass. The whole thing reminds me of imported HO brass from the '70s: made for looking at and not running. If you have a lot of money and at least 5 years left to live you could send it to this guy:
http://www.rodmiller.com/drives.html
Sorry to see you're having trouble, hope you get it solved.