That's the nicest Goldstar I've seen for a long time!
If you get fed up with it, I'll look after it for you.... :lol:
Probably an 84 or 85 ST50, from what you have said. Inside the body cavity, there will be a stamp, like this one:
This gives you the code for the colour, and other things too. In this case, it's MG - Metallic Green. Do you know what that stamp on yours says? A pic would be interesting to see.
The thing I don't understand is that it has the 50 sticker on the back of the neck. The ST50 was the standard model in the range, and most Goldies seem to be 50s. They came in a limited range of colours - the custom colour models (that's most of the metallics) were known as the ST55, and had a 55 sticker. Apart from ther colour, an ST55 was identical to an ST50. Yours looks like it's a custom colour, though I'm not sure which one. I don't understand why it isn't an ST55.
It's nothing to worry about, it's still a great guitar, but that puzzles me a bit.
Anyway, gorgeous guitar - look after it - or send it to London! :lol:
Mike