how to grease center joint on front drive shaft

i think this is oem because im dealing with a stock driveshaft.
im running a front drive shaft on my rear with the sye kit. sounded like u joints were bad, it was the center sperical joint, so i replaced it, it worked great for about 600 miles, then the sound came back, took it apart and the center joint is completly toast. before i put another one in, how do you keep those lubed? i dont see how you can get grease in them once its together.?

98, 231, AW4

On the slip joint of the drive shaft there is usually a grease nipple to grease up the joint. Only thing you want to make sure of is that you don't grease it like your typical ball joint or tre as in until you see a slight amount of grease coming out. If you do this then it will cause what's called hydro lock as in when the shaft moves in and out it will cause suction and more problems. Usually when greasing it up 2-3 pumps will be sufficient.