1998 Dodge Dakota Front ball joint

I took my vehicle in for service the other day and a technician told me one of my upper front ball joints is completely dry. The ball joint has no fitting on it and cannot be greased. It is a contained unit and should not need replacing unless there is a leak. I have not looked at the ball joint yet. If the ball joint needs to be replaced how soon should I do it? Can I wait until I hear some noise or there is a problem with the steering? Any idea what something like this should cost? Thank you for any help in advance.

Mike