HP-29C Key has no 'click'?

[Tom Flatterhand]

I recently purchased a beautiful HP-29C on eBay. It looks like new in almost all aspects. Even the keys all work perfectly. Except for one: it is the '-' (minus) key. It too can be used perfectly without bouncing, but it lacks the smooth 'click' when pressed. My questions about it:

1. does this occasionally happen with Hewlett-Packard calculators?
2. does it indicate heavy use? Because the calculator does not do this in any other way.
3. can I fix this in a simple way?

With kind regards

Thomas Ell