You've got more trouble than just seals...The pinion bearings wear which
causes the seals to fail..ALSO the gummy-yummy 90wt final drive oil causes
slow valve action in the valve body which can lead to burned out clutches..
at the minimum, you will need to check and retify any final drive bearing
"slop" and SHOULD overhaul the valvebody and maybe the whole transmission.
AND...when is the last time you (or the PO?) ever checked the oil level in
the final drive?....Hmmmm....that's what I thought.....<grin>

Steve

"Hey! nice Jeep, Mister! "
"Look kid, it's NOTAJEEP! "