Corrostop is a chemical in the cartoon portion of the Generation One continuity family.
Invented by Perceptor for the purpose of removing and preventing corrosion of any form, corrostop is the only known cure for Cosmic Rust. It is a clear blue liquid, which can be applied to a surface by pouring or spraying.
The Transformers cartoon
The Autobots used their initial batch of corrostop to coat the Statue of Liberty. While the work was underway, the Stunticons kidnapped Perceptor and took him to Decepticon Headquarters, where he was compelled to help cure Megatron of a cosmic rust infection. A small sample beaker of corrostop that Perceptor had on his person proved to be enough to cure Megatron and any other affected Decepticons.
Unfortunately, after the initial batch was exhausted, Cosmos and Blaster discovered that the supply of the key ingredient, Ingredient X, had been completely used up and could no longer be found anywhere. Fortunately, after Megatron attempted to spread the Cosmic Rust amongst the Autobots, they were still able to use a matter duplicator to create a large enough supply from scrapings off the Statue of Liberty to cure everyone who was infected.