I can’t believe when I saw this topic come up...well resurrected in this case.
I sold my entire MPC collection over 25 years ago and I do remember my PC GG1 having one truck with metal gears and the other having plastic gears. I never really ran it much so I could have cared less...I cared even less after the collection was sold.
I did recently replace (for about 22% of what I paid for it in 1987) the MPC 783 Hudson and about 3 years ago I bought a small to midsize postwar collection that had some pieces that I wanted to upgrade in my existing collection. In that collection was one MPC item a 8850 GG1. I didn’t think much of it so I took it out of its box and placed it on a back shelf and forgot about it until last Sunday night when I was rearranging some stuff on the display shelves.
I put it on the track (bone dry) and needless to say it ran awful so I put it in the foam cradle and started to tear it apart to clean it up and grease it. I couldn’t believe when I saw the bottom of the armature shafts peeking out of the bottom of the trucks when I removed the pickup rollers. I thought for sure this this thing had hundreds of hours on it and ground through the trucks. I continued to service anyways and was surprised to see it ran just fine after I finished it.