Kroil is P E N E T R A T I N G oil. It penetrates into tight spaces. Seriously good stuff; even for capped lug nuts. See below from their website.
"When it comes to freeing corroded items in tough spaces, nothing rivals powerful, industry-proven Kroil penetrating oil. Used and trusted by pros and experienced DIYers alike since 1939, Kroil quickly loosens rusted nuts and bolts, frees frozen shafts, pulleys, and more. No space is too tight to reach, thanks to Kroil’s ability to penetrate into spaces as small as one-millionth of an inch. Corrosion meets its match, as Kroil dissolves and prevents rust, cleans and lubricates, and displaces moisture."
