rear u-joint

If you are experiencing a vibration, and you found the u-joint grease fitting is missing, it would be best to remove the driveshaft and check both u-joints for binding during movement before installing a new grease fitting. I have seen plenty of them show no signs of in/out, up/dn play, yet binding during operation. A not so time consuming operation for piece of mind chasing the vibration down, and ruling the u-joints as a cause