...Something I have noticed is that some of my more recently purchased coaches seem to be 'bowing' upwards in the middle. I don't recall buying them like that as I check them.
This is still very much an investigation in progress, but I am not 100% convinced that some plastics stand up terribly well in our climes. It is interest to note that all the 'old' stuff from the 1970's and 1980's (Lima, Hornby, Airfix) all seems to be OK. It's almost like plastics changed after that to be less 'climate tolerant'...
It wouldn't much surprise me, former colleagues dealing with polymers were forever having to qualify new formulations for production of injection moulded components, because they had received notice that supply of polytetracorbynawfulamide was being discontinued, as one of the precursors had been shown to cause spontaneous brain explosions in rats fed 2 kg of the stuff per week...
...I found that the wheels on some loco's have problems. One Triang has rust, a couple more Bachmann have corrosion and a couple of Hornby's have what looks like the chrome bubbling. All of this is on the tyres where they contact the railhead. They are all steam loco's by the way...
Had the Bachmann and Hornby locos been run quite extensively previous to going into storage? Both of these brands current products have plated tyres, and it does wear through with use, see below. (The Triang could have sintered iron wheels or possibly steel tyres, now these will rust, but it polishes off.)
My oldest Bachmann models of current production type (not the old split chassis models, which were worn out pretty rapidly!) are the WD 2-8-0's, and after 23 years of regular operation, now have some of the loco tyres showing a streak of copper plating from railhead contact, no operational deficit resulting.
Likewise my oldest Hornby, 8F 2-8-0's and a Q1, now 20 years old, some of the tyre plating has worn through to the brass by railhead contact, (the tyres are presumably made from brass) no operational deficit resulting. On these, while doing routine oiling of the rods I have observed in the past few years the plating 'curling off' in tiny flakes