When looking at 5135cx1 vs 5135c01, the description mentions different colors
for the wheels.
5135cx1 = Pearl Light Gray (PLG)
5135c01 = Light Bluish Gray (LBG)
The image in the catalog seems to show another difference: the button on the
top.
5135cx1 = transparant yellow button
5135c01 = solid green button
In a bulk lot, I found three of these locomotives, all in yellow.
The first is clearly 5135cx1, as the wheels are clearly Pearl Light Gray.
The button on top is trans yellow.
The second has wheels in Light Bluish Gray (100% sure, it's distinctive
when comparing with the first one) and has the trans yellow button.
The third has wheels in Light Bluish Gray (again easy to see when comparing
with the first one) and has the solid green button.
The problems here are:
1. It's unclear wether the button plays a differrence in catalog identification.
2. The item 5135c01 doesn't seem to exist in yellow. At least not in the
catalog, as there is no set reference that has this part in yellow.
I don't know how to list them correctly.