See:
http://www.unc.edu/~melchert/molybdos.pdf (or corresponding html).
"Greek 'molybdos' is derived from Lydian."
Melchert traces the Mycenaean word to a Lydian color term, and
rejects a relationship with Latin 'plumbum' or Basque 'berun'.
Sounds plausible to me, but would like an expert opinion.
Dan Milton