Got any pictures of the gas cap?
Where about in WI are you? I'm in MN just north of Minneapolis, maybe if you're close could meet up
PM me your cell # and I can send you photos; its a black base with a blue cap. You can kind of see it I the pic I posted.
I'm also near Madison, so meeting up would be tough but shipping would be cheap/quick. The cap would fit into a flat rate envelop for probably like $8.