When George confronts Don (the mechanic) alone in the shop you can clearly see "SAAB" on the left front of the mechanic's shoulder. Every other time he is seen, his mechanic's uniform does not have that "SAAB" patch.
While Kramer was hitting on the women during the test drive there is a huge Tweety Bird in the backseat. Throughout the rest of the test drive the stuffed toy is not there.
While George was complaining about the mechanic he said he wanted his 75 cents back but the candy bar was priced at 50 cents.
George's Twix bar is one of several shown in machine, yet when he accuses the mechanic of eating it, the Twix slot is shown completely empty.
Instead of creating the lineup George should have just eaten those Twix bars. But it's also within George's character to do something out of spite, without realizing it's a Pyrrhic victory at best.
George (Jason Alexander) says the mechanic has a short name and tries to remember it, although the only name tag the mechanic was wearing said "Saab." Since he can't remember the name, it's not necessarily a goof. The fact that it wasn't actually a name may explain why George can't remember it.
George (Jason Alexander) shared a story about his father buying a Le Car, but he repeatedly pronounces the French word, 'le' as 'les' (pronounced lay). Both words mean "the" but 'les' is plural.
When Jerry calls Elaine on the phone and she agrees to come back to the dealership only if Jerry would pay for her taxi it would be an expensive fare, because when Kramer is taking Exit 15 with the dealership in site; The exit sign reads, The Pelhams, which is 20 miles North from the Upper West Side of Manhattan. Also how did Elaine get home so quickly when she first left the dealership.
The 50 cent/75 cent candy bar. Could it be George is so tight he tried to get an extra 25 cents because he felt disrespected. So it likely an error but George could have been trying to get an quarter for his troubles.
Elaine agrees to go back out to the dealership if Jerry will buy her lunch. But it can't be lunchtime because when Kramer is on the test drive with the salesman, it is dark outside.
When Jerry is on the phone with Elaine, he smacks the phone cradle with the receiver and Elaine pulls the phone away from her ear as if it hurts. This makes no sense, as smacking the receiver of the phone wouldn't make any sound on the other end.
After the car ran out of gas the green screen can be seen out of the driver side window.
George does a "candy line-up" with 10 unwrapped candy bars, but never had either the change or dollar bills to buy them all.
Before he buys the candy bar, George tells Jerry that he only needs one more nickel. Once he has the coin from Jerry, he inserts 3 coins into the machine. Later, the camera zooms in, revealing the price of the candy bar to be 50 cents. Three coins minus Jerry's nickel is 45 cents, and there are no two coins that add up to 45 cents.
George asks the cashier back for 75 cents to repay him for the Twix bar that the mechanic stole, but when the camera gives a close up earlier on the Twix bar dangling from the machine, it was only 50 cents.