I think the key thing you have said (twice so far) is that it "takes great pictures." If neither the coating or element separation/fungus looking defect, non the littler spot above it, are affecting that central super sharp area on the Helios, neither problem might be causing problems. They might even be adding something to the quality of out-of-focus vignetting that a wide open Helios offers. Some Helios fans have a stable of them, you know, perhaps because each may offer different rendering, depending on defects like that or hairline scratches on the front element, or different iris blade counts....etc.
If it "takes great pictures" do you really want to monkey with success? Just buy a few more Helioses. I, personally, would wait until I found one that was just so-so to practice repair on, not one that, to quote someone in this thread, "takes great pictures."
Originally posted by timw4mail I do have another in the mail, with a modified square aperture
As far as Russian lenses go, I've got two Zenitars on the way: a 50mm and a fisheye.
Regardless of the defects of this lens, it still takes great images, so I'm not especially eager to tear it apart. (Plus it has the zebra focusing ring, I hear those aren't as common)