Scraplet

Scraplets are alleged to be the deadliest disease known to mechanical lifeforms in the entire galaxy. A single scraplet resembles a tiny robot that can transform itself into something that appears to be a harmless nut or bolt, but they can self-replicate with incredible speed and embed themselves en masse into the skin of a mechanical organism, and over time, digest the victim nat by nat.

There is no known cure for scraplets other than a legend that claims a "rare chemical" was found that could kill the scraplets.

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This "rare chemical" was water.

From Teletraan I: The Transformers Wiki, a Wikia wiki.