I've got an old oxygen sensor and an old front exhaust manifold. One can look at a spark plug to see its history. Does that hold true for any other parts?

History aside from, "this part definitely earned its pension," of course.

Not much to read on a O2 sensor other then color. Black rich, white lean, gray good.

Depends on the O2 as well, a front one black/sooty can be a clogged cat.

First thread, black. Bulb, pink and white. Tip of the bulb, bluish-gray. Guess it saw a lot before retirement.

Kind of light indicates slight leanness... Makes sense, my fuel pump is getting tired (42 psi, 60K miles ago).