Red Sub Mark IV 1680 Dial

[grapepudding]

Hi Rolex Forums,

This is my first post but I have been a long time viewer so please be gentle.

I was looking to buy a 1680 Red Sub and came across this example for 20k USD. As this is my first major vintage purchase (I am a noobie), I was hoping to call in the experts!

Please feel free to critique my evaluation.

From what I can tell, it's a 2.4MM serial Mk. 4 1680. Hands and dial seem original and matching patina, the pearl/pip has been replaced and glows under UV light (unlike the hands/dial). Caseback is stamped 1-70 and the bracelet is 1-71.

I understand that Mark IV dials generally started at the 2.45 MM serials however I've seen examples on the forums in the 2.37 range. If you have any feedback or corrections on the above, I'd greatly appreciate it. Thanks!