Talked to a guy with a '56 sedan & he says that if he lets up on the gas pedal a little when it's time to shift, the tranny will shift ok, but if he doesn't, it will slip between the 2 to 3 shift. Does this sound like a linkage adjustment issue, or time for a rebuild issue? He said he keeps an eye on the fluid level, but didn't mention whether the fluid smells or not.