It's a little late for a reply to this thread, but here goes anyway. I have a photo of Derks control panel. The button is very similar to the Lucas ones you guys have shown, except the actual button portion is actually steel, as you can see by the pitting.
The button still has it's spring action, and appears as though it can be dissassembled and cleaned up.
The panel is a nice find. It also has all three of the origional light switches at the top. They are an interesting open knife type switch in the back.
See, there are advantages to living in this deepfreeze called Manitoba. Things stay reletively preserved here, even when stored outdoors in a swamp.