Now guitar manufacturer Karl Hoefner, based in the southern German state of Bavaria, has launched a global hunt for the instrument.
"Most probably, the bass was stolen," said Hoefner's Nick Wass. "It has been gone for 50 years. Now it's time to find it."
He told dpa that there are several rumours swirling around the music industry. "But they are only rumours."
McCartney has been informed of the initiative to find his long-lost bass, his management in London confirmed.
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