This is my favorite lens of all in spite of all the visible aberrations, limitations, etc. It's totally NOT deserving top spot. But it does. I am not sure why. Mine doesn't get that much onion ring. Double check the very edges of the lens rear and front element. Since these are very old and usually not receiving the proper love and attention, and pampering and patting and soft words they deserve, many times they accumulate dust in the very outer edges near the rim. And this exacerbates any onion ring (well, only out ring). If it's not that, then may be differences between the few versions of PF 58 1.4
Looking at the front and rear elements, I could see a few specks/tiny spots, but nothing around the edges. Just to be thorough, I took a cleaning tissue and ran it around the edge; it came up clean. So I dunno.
Another example (especially on the left/right edges of the bush in the center background, at 100%):

Pen-F, MC Rokkor-PF 58/1.4
This lens, if you stop down to 1.6 improves quite a bit too. But I like that it's soft at 1.4. Then I don't need to constantly swap lenses, as it becomes prety sharp by f2.8 and vignetting mostly gone.
Yeah, I only saw the prominent rings when shooting wide-open; stopping down a notch or two cleared them out.
I was mostly just amused at finding the soap-bubble look on the 58/1.4 after people praising lenses like the Trioplan for it. Heck, for artistic reasons, I'd like to see if I could duplicate the effect in the above pic (the pinpoint source surrounded by the ring) at a larger size across more of the frame. Probably gonna have to wait for another day, though...
Did you try using it for portraits (or rather, people) around twilight or night with low light illumination? Make the noise high, to see if you like the rendering. I use this lens most when it's night and there's all kind of dim lights around. For me it shines at night with low ambient light.
Honestly, I don't really do portraits; I'm uncomfortable photographing strangers, and my family is pretty camera-shy. ^^;; I'll have to give the low-light a try, though.
As I said, I was disappointed the prior time I tried the lens with landscapes, and I wasn't impressed with the distance shooting I did with it this time either; it seemed to work best with subjects at short-to-medium range (around 10-15 meters, or less), and single subjects instead of a broad field. Has that been your experience?