Not sure what you mean by slack. The flange bolts to the output shaft which is splined so the question is, which direction is the play? Is it wobbling on the shaft, loose fore-n-aft, or is the play rotational - like if you were just feeling driveline slack within the transfer case/transmission?

The seals go bad from time to time and are not too hard to replace.

-Bill
'87 4Runner w/ '96 5VZ-FE, 'Red Chili II'
'97 Taco XtraCab 3RZ-FE, 'BlackBean'
TLCA # 13257, Rising Sun 4x4 Club Land Use Coordinator
"He who stops being better stops being good." -Oliver Cromwell