UK Car Jokes

The other day I was in the local auto part store. 
A lady came in and asked for a seven ten cap. 
We all looked at each other and said, "What's a seven ten cap?" 
She said "You know, it's right on the engine. Mine got lost some how and I need a new one." 
"What kind of a car is it on," they asked? Now I'm thinking maybe an old Datsun Seven Ten but no, she said its a Buick. "OK lady, how big is it?" She makes a circle with her hands about 3 1/2 inches in diameter.
 "What does it do?," we asked. 
She said, "I don't know, but its always been there."
One of us gave her a note pad and asked her if she could draw a picture of it. She makes a circle about 3 1/2 inches in diameter and in the center she writes 710. 
The guys behind the counter are looking at it upside down as she writes it...and they just fall down behind the counter laughing so hard in hysterics. 
One guy said, "I think you want an oil cap." 
She said, "Seven Ten cap, oil cap, I don't care what you call it, I just need one, and I don't see what is so funny about it." Yes, she was a blonde.

Note: If you read "710" upside down.... it is spells OIL!!