Near the very end of the film, Old Sun starts to spin around before he is actually shot.
At the start of the movie, when the attack on the generals' camp begins, the first general points around a map saying, "According to our intelligence reports, the Japanese are here... here... here... & here." However, he is pointing around a map of northern Canada.
Early, when Capt. Don Wen is offering Billy the job, he says "Old Sun's in... There's money in it." Billy's response is "If Old Sun and Lightnin' are in, there must be money in it. Count me in, too." Capt. Wen never mentions Greased Lightning previously, meaning Billy is replying with information he couldn't possibly know.