Yeah, there is some kind of little seal that needs to go on there. If your slip yoke splines are worn too bad, then it won't seal properly. Sometimes it will actually slide down on the splines and you'll see it hanging out a little bit. Check out the vendor forum on this site. There's a company on there advertising slip yoke eliminators for NP205s and NP241s. I think it means NP208. That is the best thing you can do. Of course then you'll have to have a new driveshaft.