The Aluminium on Aluminium surface can pick up especially in humid or large temperature change countries. As said you can knock the pin out after the set screw is taken out. But just teflon oil should free it up if you work it back and forth without removing the pin.
The Intairco Wheels to AT legs always need a 6mm washer between the brake unit and leg to give tyre clearance.
Once free, ground handling is better if you wrap the leg and spring with insulation tape, 4-5 layers. The spring will still operate under the tape, you can also tie the brake line to the rear outside edge of the leg with an additional wrap of tape.

Dave