yes you can regrease it, if you put geaseable joints in it, if not then most likely they are non-serviceable, and need replacement. Life-time greaseable my a$$. Maybe in a dry state where you don't drive during rain, snow, in the dirt, but still doubtful. I just did the joints on my front driveshaft, including a new centering joint. On a 98 you can get a greaseable centering joint/yoke assembly(imagine you can get it for other years), uses a needle fitting, and then I used greaseable u-joints for everything else, needle fittings when possible, makes life easier.