2000+ Town, Trains, Buildings, etc

[Philippe Hurbain]

String modified with paint because studio not correctly rendering it.

Yes, problem is that Studio photorealistic renderer doesn't like scaled parts (their POV implementation works fine). My guess is that they shrink parts a bit (to create fake seams) before scaling the part. The fake seam width is thus multiplied by part scaling!
Instead of long 4-4cyli, you could use many aligned short length 4-4cyli with some overlap. But why didn't you simply use LDCad flex part? You have to tweak a bit parameters to avoid the same scaling problem, but it can be done easily...