Indeed, the only current Nikon super tele with Electromagnetic diaphragm are the new 400mm f2.8 E and 800mm f5.6 E.
Of course I di expect Nikon to update the 200mm f2.0, 300mm f2.8, 500mm f4 and 600mm f4 soon, but that won't help the OPs issue.
Sending the lens for repair may be the best option. The only major failure I experienced with a Nikon item in ~30 years of merciless usage was aperture related with a 70-200 f2.8.
Cheers,
Bernard