EARL,
THE FORD 9 INCH IS THE EASIEST DIFF ON EARTH TO WORK ON. YOU CAN BE LEAKING 90W FROM ANY OF 6 PLACES, ALL ARE EASY TO FIX
(1) - YOKE - REMOVE THE DRIVESHAFT, LOOSEN THE HUGE NUT HOLDING ON THE YOKE, PRY IT OFF & REPLACE THE OIL SEAL
(2) - 3RD MEMBER - JACK UP THE TRUCK, REMOVE THE BRAKES, REMOVE THE BACKER PLATES HELD ON BY 4 STUDS EACH, PULL THE AXLES, REMOVE ALL THE NUTS HOLDING THE 3RD MEMBER TO THE REAREND CASE & PRY THE 3RD MEMBER OUT. A QUICK BEAD OF SILICONE WILL SOLVE ANY LEAKS. EVERYTHING GOES BACK TOGETHER THE WAY IT CAME APART. 9IN 3RD MEMBERS ARE DROP-OUTS, SO NO ADJUSTMENT IS NECESSARY. WHEN YOU BOLT THE AXLES BACK INTO THE HOUSING BE SURE TO REPLACE THE GASKETS BETWEEN THE AXLE FLANGES (3) & HOUSING. THIS A VERY COMMON PLACE FOR LEAKS. THE OIL SEALS ON THE AXLES THEMSELVES (4) ARE ALSO EASILY REPLACED. OTHER PLACES OF POTENTIAL LEAKS ARE THE FILL PLUG (5) AND THE BRAKE JUNCTION BLOCK (6)THAT THREADS INTO THE DIFF HOUSING. HOPE THIS HELPS. ONCE YOU'VE DONE THIS 100 TIMES IT GEATS EASY.