Good chance you can clean the solenoid and get it working again. They get lube built up inside and don't let it cycle like it should which is what yours sounds like it is doing. There are some small pieces inside that can get lost or damaged if you are not careful, but if you are going to send it to be replaced anyway it might be worthwhile for you to try to clean it. There are threads about taking humphrey solenoids apart.
My WTB/Trade thread
For God does speak—now one way, now another—though no one perceives it. In a dream, in a vision of the night, when deep sleep falls on people as they slumber in their beds, he may speak in their ears and terrify them with warnings Job 33:14-16