Jack sells the family's Dodge Polara station wagon. A sign identifies it as a 1963 model, but the grown-up Kevin narrates that it's a nine-year-old car, making it (at the time) a 1960 model. In fact, that particular car was a 1968, hence the required by law side marker lights. Also, the "brand new" red Dodge Dart convertible purchased by the neighbor across the street is ironically a 1967 model, making it two years old.
1968 Dodge Polara wagon is introduced as an old car, being in Kevin's family for years. However, in previous two seasons, the family drove 1963 Chevrolet Impala.
The car of Arnold family was in fact 1968 Dodge Polara, so it was by no means an old car in 1969, when the action takes place, and it could not look so obsolete and break down as much, as it is suggested in the episode. Besided, Dodge was more prestigious brand, than its replacement Ford.
This episode is set in 1969, however the song "I Can See Clearly Now" by Johnny Nash was not released until 1972.