Hello Mathias and Kwakers,
I wonder if this may just be extra flashing.
On close inspection on my models I think the braces are the same thickness. What makes one look thicker than the other on my models is caused by a small amount of flashing that has not come off in the tumbling process. Some cab castings are crisp but others not. If you look at the brace from underneath or at an angle you may see the rough edge I am referring to. When viewed straight on they look to be different sizes.
Easy to see with an eye loupe
I have looked at the horizontal section between cab and gear cover on the RW models. The last casting with the rear braces on the regular wheel model look to be the same size as the early RW casting and look to be the same as my SF 21 Foden models.
I would say the brace is about 1.00mm thick but difficult to measure as most vernier calliper jaws are too thick to reach accurately. The other thing that occurs in this area is paint run or build-up. A word of caution that vernier calliper jaws are very hard and can easily damage paintwork.
Having said all that, I would be interested to know if the one Mathias shows is thicker all the way through and not caused by edge flashing or just extra paint and what the thickness is.
Very nice picture Mathias, thank you for showing, hope you do not mind me adding a few words to show what I mean.
All the best for 2015