It's just a super simple clutch. Take the rod loose from the rotating square shaft (pull out the cotter pin)  you should be able to pull the rod and force the clutch to seperate the gears. If you can't do that the shaft with the gears is "gunked up" with krap. You can take the clutch apart it's super simple, pull the spring retainer and the spring will come free, and clean the shaft so the gear will slide against the spring and against the ground drive gear.

The square shaft doesn't turn all that much in relation to the disk arm travel.

When adjusted properly the gears should just disengage from each other when the square shaft has the disk arms all the way up. If the holes are worn in the plates that the clutch throwout rod sits in that's just enough to not allow the clutch to disengage. The throwout rod comes forward (toward the tractor) when it is disengaging the clutch.

The metering system is tight for a reason so it's not going move easily. Plus if the drill hasn't been cleaned really good every year and the drill's exposed to moisture it will be hard to adjust the seed metering.. Take a small bar, (anything to hold the metering notches away from each other,, and with a hammer tap the metering arm back and forth to free it up.  I thourghly blow mine out the instant I'm done planting. I get every speck of grain,dust, whatever out of the seed flutes.

When I say "tap with a hammer" ,, just moderately tap the spring steel arm back an forth till the seed flutes move more freely. I would highly suggest NOT putting any penetrating oil, etc.. on the seed flutes unless you *completely* get all the oil off after getting the seed flutes to work. Otherwise,, you will have a gumed up mess with dust, seed, etc,, which will even be worse than what you have now.