First of all does the armature more freely through the coil manually? Can the sleeve be easily removed from the coil? If not the coil could have overheated and melted the sleeve.
Is the armature rough or damaged?
Does the coil function properly in solenoid test?
Is the controlling transistor on the power board OK?
What is the dc output at the coil vs the power board?
Just replacing the coil may not fix the problem.