After dinner tonight we tried a different station. Talk about service! They directed us to the right spot--only certain pumps have diesel. They politely informed us that for an extra 100 baht, I could get a free T-shirt,which we did. (Thai sizes being what they are, well, at least Jacen can wear it.) And they even gave us a free Thai lesson, correcting my pronunciation of the word for "hundred" (it's more like "loy" than "roy").
Yeah, we'll be going back.