A friend has a 02 F350 with a 10.5 in. limited slip diff. He is experiencing some chatter when starting off and turning at the same time. He went to change the fluid but the Ford owners manual recommends not changing the fluid as a maintenance item. The fluid lasts the life of the vehicle. I know a change would not hurt but, the fluid and the additive cost 140.00 from the dealer (all synthetic). I think he should leave it alone and see if it gets worse.

It should be changed and you can get the limited slip additive at most parts stores instead of the dealer.Same with the gear lube,most parts stores sell it too.

yeah avoid the dealer until you can't get it elsewhere.

it should be done every 30k