For several reasons…

1 – I’ve received lots of encouragement and suggestions to address the problem of the Tricky Truck under the baggage-mail car. Thank you, everyone, for the help (and for bearing with me).

2 – I think I found the problem – a very, very slight misalignment of two rail ends at a gap. I tweaked, added an extra spike, and things are better for now. I will still experiment with trucks to see if I can get the baggage-mail car to track more reliably, too.