I have an 85mm f1.8 from about 1975 and a 105mm f2.5 from 1971, and they both exhibit the "stardust" in your picture. On very close examination I think it is in the glass, and can not be removed. I've used my two lenses for years and years without even noticing the "stardust", and have never noticed any problem with the images. I would leave it alone.