It seems that most popular titles have at least one expensive part that is considered crucial for gameplay but for which replacements are not generally available, except as a big dollar NOS on Ebay. For example, Creature From the Black Lagoon has the hologram.

What other parts are impossible to find for various popular titles? For example, it could be a ramp or a motor. However, we don't need to mention plastics that are purely cosmetic - these always seem to be hard to find (except for the most popular titles) but most of us can live with the problem.

Maybe this list can spur product creators to do something.

I'll add another: the Theatre of Magic trunk motor

This might be the exact opposite of the pay-it-forward thread.