Hello, I have a couple of what I believe are original oil caps for 65 to 67 big blocks. My question is that the S in the middle of the cap on one of the caps is curved while the other S is squared where it almost looks like a # 5. The rivets on both caps look alike and the washers are about the same as well. I was wondering why the S' would be different unless on of them is a service replacement or repop. BTW both caps have the sm logo by the S. Thanks in advance.