Rust-B-Gone

Rust-B-Gone, named Oil in the original release, is a key item that appears in Final Fantasy Adventure and its remake, Adventures of Mana.

Final Fantasy Adventure/Adventures of Mana
Sumo searches for a way to reach Glaive's Airship after Fuji has been kidnapped by Julius. Unfortunately for him, the only way to get through a rugged terrain is to get into the Gaia Pass, whose entrance houses a sentinent entity called Gaia. The earth spirit spits the hero out upon entering, forcing Sumo to detour to the Dwarf Cave where he learns that the nearby Forbidden Mines houses veins of Mythril Silver deep within. Our hero ventures into the mines, but cannot proceeds any further as a rusty old minecart won't budge on its tracks. Turns out an Oil Peddler is nearby and offers to sell his Rust-B-Gone for 500 GP. The hero purchases the item and heads back to the mines, oils the wagon wheels, and rides the cart in search of the precious metal.