I was presented with one first up that appeared to be a motor burning out going by the smell from it. However on further inspection of the model I found the flywheel insert problem the smell being from the plastic melting due to the friction from the flywheel. Also you would notice that a perfect running loco now has bad running or none at all. So if you have any problems like this then check these out and some glue of whatever you favour should do the trick, you might need to add something between the insert and the metal flywheel though depending on how bad it is. Some tissue or 010 thick styrene sheet or strip might do the trick though.
I am not saying that they are bad models or something as I have plenty of them just pointing out a fault that is not obvious once the unit is opened up, you just do not think that this can happen, so you do not check it out, I found it accidentally, but unfortunately it does happen. So if you suddenly get one of these models and it does any or all of the things I said check out the flywheel plastic inserts as that is the problem.
Oh yes I have informed the company of the problem as well.