There was a SF novel in my high-school library (sometime between 1985 and 1990), that I had intended to read, but for some reason I never got to it, or maybe it disappeared from the library. English language. I can't remember the author or title, or the name of the main character, but the gist of the back-cover blurb described the story a something very roughly like this:
[So-and-so] is a clone. A clone's personality is unstable, and degrades over time... but [so-and-so]'s personality seems, unusually, to be "rock solid". So she goes on a quest (or something) to discover just why that is.
That's just my paraphrasing of what I can remember (obviously). They key point is that the protagonist is this cloned woman whose mind ought to be degrading somehow, but for some reason it isn't. Does this ring a bell for anyone here? It's bugging me that I can't remember it, and I still think it sounds like it might be an interesting read.
I'm pretty fuzzy about the cover art, but I think there might have been a double helix on there, and a female silhouette? I don't trust that, though - I think I'm too likely to be mixing it up with other books I've read or seen, so don't take that as a reliable clue.
C. J. Cherryh's Cyteen has occurred to me as a prominent SF novel with a story based around cloning from around that time, and I suppose it might have been that, but I don't think it's really all that good a fit for the blurb as I seem to remember it.