I know this is not a rocket-science question, but;

What is the likely culprit that keeps my 1899 cocking indicator from working, (firing pin, hammer, and sear, etc, all working properly)?

I can't recall the last time I had an 1899 bolt torn down,

Thanks,

My first guess would be the wear on the bottom of the indicator itself or on the firing pin ( the actual part that threads on ). I don't see anything else it could be. A lot of metal on metal contact going on.

I had one that was frozen in the cocked position by old caramelized oil. Took it apart cleaned it up and worked fine.

Hmm. I don't see how that's possible unless you have a version I haven't encountered ( very possible). On all the types I'm familiar with, it's metal against metal contact that brings the indicator back down. You can even see the witness marks on the firing pin mechanism. It doesn't depend on gravity to show uncocked position.

I had a 1899 that the cocking indicator did not work because of wear at the back of the bolt where it locks up. It also had headspace issues. Closing the action with a feeler gauge slid in behind the bolt was enough to make the cocking indicator function. I can not remember the thickness i used.

My experience has been more often than not, the rifle has been disassembled and then reassembled with almost all of the parts.