Place a new u-joint with the bearing cups removed in the differential-side flange of the half shaft. Be careful when you remove the bearing cups, as they are lined with needle bearings which can fall out fairly easily.
For safety's sake, a new trunion was obtained from Zip Products, shown here prior to giving it a coat of Rust Oleum Satin Black.
You can use a 7/8" socket or the Zip tool to sink the bearing cup down just slightly below the groove that holds the snap retainer clip.
Use needle-nosed pliers to install a snap retainer clip over the bearing cup so that it seats in the groove of the flange.