Following up on this, since we're talking about lock hubs, I could use some help since it looks like I need a new one. I thought I was missing the cap to one of the auto lock hubs, but it turns out I'm missing the whole thing (according the guy whos doing some work on it).

The 4x4 is working though, all 4 wheels spin when in 4H and on a lift, but since I'm missing the auto lock hub, does that mean that the wheel is stuck on the lock position, and the front axle is turning all the time, even when in 2H?

Since I'm missing one anyway, it seems it's time for a new set. Questions are:
1) should I look for an auto set, or a manual set?
2) where should I be looking & can anyone recommend a specific make/model?
3) how easy or hard are these to replace for someone with limited knowledge and limited access to tools?
4) if it's been stuck in the lock position, have I done any damage to the front axle? extra wear and tear, or just extra gas usage?

Thanks