Just the take spacebar off and troubleshoot it a little. Not worth the shipping costs if the problem is simple. I think I know exactly what the problem is.
1. Take the key off
2. Check the switch itself. The action should be smooth like your other keys. (Take off another key and test that switch directly to compare if needed.)
a. IF the switch is bad, RMA it.
3. The inserts should be pointing towards the top of the keyboard with the spacebar facing down, but like RColinTaylor said, probably not the issue.
4. Look at the black clips that hold the stabilizer bar. There is one on each end. You'll see two black tabs that stick out perpendicular to the base plate. I bet one of these clips is slightly warped and the space between the tabs is closer on one, or even both sides. This would case the tabs to "grab" onto the inserts instead of just guiding them up and down. Just bend the tabs apart and hold it in the position for a few seconds. Repeat if necessary. This should open up the gap and allow the key to travel freely. Not critical, but you can grease it as well.
Pretty sure 4. is going to be your solution.
