Intermittently unresponsive key on 17" MacBook Pro

[chrishatch]

The "o" key on my 17-inch (Late 2007) MacBook Pro is unresponsive about half the time.

If the key is struck 10 times, perhaps 5 o's will appear. None of the other keys have this problem.

It seems that to fix this, I could either:

1. Replace the key (individual keys are available on eBay)
2. Replace the keyboard
3. Replace the entire "top case"

I'd rather not go overboard if there is an easy repair.

This problem disappears when using an external USB keyboard.