Yeah, it's a real nice setup with plastic gears! Anyway, possibly this will help Lippert Venture Motor 18:1 Replacement Gear Set
I think there is a poster on here that may have just the nylon secondary gear for sale, I think he had to buy like ten of them, try a search for "venture" or "lippert" on this forum.
If I remember correctly the two thrust washers go in font of a behind the gear, and there is a washer to take up the lateral thrust on the gear. Hope this maty help.
Dave and Rainy