Ford used to offer a penetrating spray that
was more or less designed for rusty seized
exhaust bolts and studs
It foamed up upon application and had lots
of moly in it apparently, because it was dark
black/grey. Of course, it worked for loosening
any bolts or nuts other than exhaust, and
it was the best or some of the best penetrant
I've ever seen
IIRC the formula wasn't something the
treehugger gubmint types liked, and I'm
thinking it's an obsolete thing now
I'm a KROIL fan for rusty things, but
someone told me that there's new
KROIL now that's different