That is an anti-backlash gear. While the gears are disengaged, take the split gear and slide one half of it against spring tension by at least one tooth and then engage it with the solid gear. Two teeth may be better if the spring allows it.
I've found the two halves of these anti-backlash gears seized together with oxidation on many occasions doing restorations. So if there already appears to be tension on the spring, shoot some WD-40, 3-in-1, or similar in there and see if they'll loosen up. You'll want to use a drop or two of proper lubricant in any case between the halves. On more than one occasion I had to remove the gear and let it soak for a day to get the halves to finally lose their grip on each other.
Grant/NQ5T