How do you finish off the parts you don't clean with isopropyl at the end? Do you just let them dry after their first rinse?
Edit: oh wow, just realized I commented on a 5 year old post. Not sure if I can delete.
Maybe the mods could move the post? Probably better than a duplicate post. I'm sure one will chime in when they come across the post.
I'm very new as well, that was one suggestion I saw in a video that was helpful, and much more gentle on the parts. Another thing I've heard which I think applies in this regard is if something feels "off" or like it needs to be forced at all, something is probably wrong, not seated properly, etc and you should stop screwing and go back a step. With the level of precision movements are manufactured to, it should feel just right.
When you were assembling the train wheels did you do so in the order indicated on page 3 of the manual? Reverse order steps 49-35 - if you get the ratchet wheel screw on you should be able to give it a wind by turning the screw to the right.