Not yet. In my dictionary, protolife (read, pre-life) is self-replicating assemblies, including prions but also tin pest and even fire. Any construct that has that seemingly self-preserving reproduction, which inadvertently causes population and sustained presence, the scoreboard of something well-evolved and adapted.
However, only protolife with variance can evolve. I'm not sure it's exhaustively impossible to see tin pest change: Consider some kind of unusual variant or alloy that is less susceptible to being eroded by water, and more importantly, populates as much and as often and either it reaches nearby environments or it is a "mutation" of some noticeable frequency. Some, most, or all tin pest would be of this variety. And yet ultimately, like GP said, this lacks real mutation, the chain of possibilities isn't there. It only coincides with sustained presence.
GP's prion is some kind of brown goo scenario, but it seems like it leans on an abundance of inert proteins, or protobiosphere. I still lean towards this endpoint because of increased variant options over tin by sheer chemistry, because "more stable" variants will probably be (inadvertently) leveraging properties that are more True Scotsman "life", like incidental locomotion. Or maybe they clump. Or, hell, I don't know, because disclaimer: I'm speculating out my ass and don't know shit about the subject.