I have never had luck with using the grease zerks. I take them apart to grease them with a molybdenum grease such as the tube provided by RCV for axles. It also gives you a chance to inspect all the pieces and make sure the grease is evenly distributed not just squirted along the path of least resistance. I have also found that they need constant adjustment to keep them where I like them. I also highly recommend burping the boots and using zipties or safety wire to keep them on. That is a high potential area to let water and dirt into the joint which will cause corrosion over the long term and pit the ball/stem along with the seating surface that mates with the top of the ball/stem. If you do have issues, I think the last rebuild kits I bought were in the $40 range direct from SuperATV who now owns or licenses the Keller brand.
That being said, they are very strong and durable as long as you aren't using them for travel stops. The holder will notch into the ball/stem and create a weak point which can be the start of a failure eventually.
