To rebuild your SY or SZ upper ball joints requires you to take a chisel and undo the Factory staking done to keep the upper housing that contains the plastic insert from coming undone. These can often be repaired and re-used but British Tool Works now has brand new stainless housings available for $75 ea.  These also incorporate a grease fitting unlike the originals.  Here's an idea - grease your ball joints!
A stainless zerk or an original brass button head fitting is available.