Question about oil seal behind the drive shaft flange in 3 speed auto

[anita@seattleu.edu (Anita Yat Man Chan)]

How long does the oil seal behind the drive shaft flange in the 3 speeds 
automatic transmission last(this is on a 85 5000s)? If it is worn does it just
leak or will it also make a whining or rubbing noise? Is it true that the 
seal are consist of metal on and rubber i.e. the inner edge is metal and the 
outside edge is rubber and the drive shaft flange rides on the metal 
inner edge. The ones on my is not leaking but I keep hearing this 
whining and rubbing noise from the front end. My mechanics said all the
CV joints are fine and front wheel bearings and brakes are fine. He 
thinks the noise is coming out behind the drive shaft flange so he 
suspect the oil seal is the source of noise. Also the final drive 
fluid level is fine, he checks it everytime when I take in for oil change(
I bought it used w 59,000 miles on it and now it has 113,000 miles on it)
since I bought it used.

Anthony Chan
(I am using my sister's account)