Same story, millerdog. I think you're referring to the oil filler cap. Replacement part for original equipment,,,,
Another good guess though, looks like I'll have to put the back seat belts in too....
Actually, it's kind of a tough question, you really have to know your old cars.
Here's a hint- it was a government mandated change starting in 1967 for all cars, not just Darts....
Cheers
Lee