If you fit Vesconite HiLube bushes and lip seals then once a year greasing should be fine. Users in Oz run over 100,000 miles with Vesconite HiLube, even with no lip seals! Some have used 'O' rings but they may actually run over the dirt and rag it into the grease.
Greasing anyway only takes less than 5 minutes. The botton nipple is the important one as it pumps grese between the bushes and into the friction/thrust bearing, the top nipple I tend IMHO to think of as unneccesary as it tends to grease the kingpin above the top bush that is lightly loaded and is reasonably protected from road dirt. Regards PJB.
