Based on innumerable web posts and (and my personal experience) modern toothed belt drives have proven to be reliable and smooth running. As others have posted - don't change out the drive if it is running well. You should know that not all Sunset and Sunset 3rd Rail locomotives were built with belt drives. Several 1990's era Sunset/Sunset 3rd rail locomotives such as their PRR S2, J1, and I1 models used enclosed worm die cast gearboxes.