The models are unfortunately dimensionally incorrect in some areas especially between the top of the windows and the rain gutter. The bogie's are over scale when compared to those on the Cravens or those produced by Replica Railways. There are also some issues with the Body sides bowing inwards in places. This is probably due to the fact that the roof is a separately fitted item, and the body suffers from the bowing, maybe from it being released from the mold.
Unfortunately there is really no fix for the dimensional errors on the coach. The bowing can be fixed by adding bulkheads to the model. It's all down to if can you live with it or can't you. I have some myself and I will get a few more standards to try and complete a rake. I hope a composite will be released as they were a very unique coach, and a super standard would be nice too. If as I have said you can live with some of the let downs of the model they do look good from certain angles. As for poor running coaches I would check the back to backs on the wheel sets and the springs for the close coupling units. Also don't run them on small radius curves.
HTH
Rich,