First - designer reply - rock on! Appreciate the personal touch.
Next - the situations I like least in games are where it's 90-95% clear that there's a RIGHT way but there's no actual instruction anyway--whether in the rules proper, supplemental examples, ancillary info such as card descriptions...or anywhere else in the game package.
Really breaks the flow of the game. Would've thought this kind of thing had come up during playtest. I can understand there's some amount of stylistic choice to be made in how to write rules--and for me this is a basic turn order explanation which as such should be in the written rules. The caboose detail would then be mentioned as an exception on the card description sheet.
It's been a while since I read the rules, but I think it IS explicit...
Loading wild: You can load a card as if it's a different type...
Load: You can put the right stuff in the right car...
So you can only put oil in a tanker, and if you discard a card when loading you can pretend that any card is an Oil.
The caboose is an exception, and I think it says so.
You can tell by looking at the board what resources people have on their train, even if you see face don cards... the only exception being a face down card in that one caboose (which is WHY it's an exception, otherwise you would have to remember what you chose when you loaded it, which is lame).