have you checked the suction in your pump?
I was incomplete with my suggestion. If the pump has lost suction, that too represents an air leak. So the pump should be included in the check.
Fortunately, water pump systems are so utterly simple, that the problem can only be a bad pump or an air leak somewhere. Start at the source and work toward the faucet. Keep in mind that an air leak in the feeder line from the tank to the pump can also be the problem.
I agree with the recommendation to rebuild the pump. I rebuilt my Par when the shutoff pressure switch failed. Theses pumps are indestructible and well worth a rebuild.