[Nonfractal]

OK, I got it.
Carrera guides are not something I use but there are some good resources available
The return spring centres the guide.
There is only one spring to return the guide to centre so its very unlikely that the cause of the problem is the spring itself.

This vid shows how to remove the guide
https://m.youtube.com/watch?v=TDxQnE8ueiI

This next one shows how to prep and reinstall the guide, ensuring free movement left and right 
https://m.youtube.com/watch?v=XpuH0xN_yqE

Looking at the youtube vids, its likely that the lockup is caused by the guide not moving freely, scuffing on the chassis.
It seems that the springs are not sold separately.
Hope this helps.
Alan