Maintenance is a chore on an exhibition layout. What we all want to do is make new things. What we have to do is fix the old ones in time for the next show.
Now I have a simple trick with rolling stock. If I take too much, anything that breaks is put upside down in the stock box and left to be mended in the future. Fiddling around behind the layout is best avoided unless you really have no choice. If you think you can drop and lose small parts on the workbench, the problems are magnified when standing up trying to work in the fiddle yard !
As it happens this wagon isn't too poorly. All it needs is a new coupling bar - 5 minutes with a pin and some superglue followed by a splodge of weathered black paint. Then the model returns the correct way up and heads off to the show.