Not exactly rare but they are harder to come buy. This should be a very early 70s 'resist' model with nicely faded blue inner bezel and a case thats in 9.5 condition. The dial shows appropriate age however but it all seems correct and has the kanji day wheel which supposedly indicates early production as well. I'm still trying to figure out a small mystery about the case-back serial. The seller claims it was fathers 30+ yr old watch and he seems very legit. But the serial dates to '69 which seems very unlikely. And some 'pogue' experts claim that in the later 70s the numbers on the case-back lost the circles and #'s were stamped in straight lines towards bottom of case-back.
So-its either a '79 (more likely) or something earlier. Either way I am pleased with it as it satisfies my reluctance to wear my '63 GMT which popped original bezel last year nearly giving me a heart attack before I found it. So I know have a 'niche' of 6139's-a silver and gold. If I get the blue one I'll have to download the Bad Co. song I used to rock out to in the late 70s
here are pics: