what causes a lil slack/movement of the pass-side half shaft @ trans outputshaft

What is your question?

Due to leaking fluid, I replaced the output shaft seal on pass-side, added a couple of qrts & the seal failed after a month. I noticed that I can move the half shaft up & down about a quarter inch at the seal & when put in R from P a slight knock. Despite the leak & knock it drives like it's a new car. What does the lil wiggle room tell you? (I have torqued the axle nut to Hyundai specs.) Do I need a new seal and a output shaft seal repair sleeve to take up slack or is a bad disc? Don't want to remove it if I don't have to. Thanks