[jleonard]

They usually disintigrate or freeze up because it is near impossible to grease them and they are in an extremely poor environment. With a length of hydraulic hose and a few fittings the grease fitting can be mounted remotely to a convenient location so it can be greased annually, then it should last forever as there is not too much load on it (unless shaft alignment is out).
Or you can add a spring loaded "grease cup", fill the cup and forget about it.