I removed the fuel tank, it was almost empty anyway .
The sticker has 503 on it .
I have a paint touch up pencil from BMW, came with the bike when I bought it 31 years ago, oddly, the paint number on it is 159, yukaturkis metallic .
Here's a link to a guide to BMW motorcycle color codes .
http://bmwmotorcycletech.info/pcodes.htmI think turquoise is a more accurate description, than blue .
I'm the original owner of the bike, so I know nothing has been changed or messed with .
I have some pictures, if you would like to see them .