Maybe it's my eyes or the angle of the pics, but it looks like the rollers are slightly crooked; some rods are bent; and the traction tire wheelset looks to be crooked.
I think any of those or the combination of all three might be causing the loco to short, especially on switches.
If you're concerned about the rollers, polish them with a Dremel and mild abrasive pad; then apply some contact cleaner; and finally lube lightly with an electronically conductive lube, like Bachman's.
