final drive lube

[CLDEPE@frmail.frco.com]

Hello All-

Can anybody Out There give me some advice on how to change the final drive oil
on my '83 5kT?  The Bentley gives me good instructions on how to completely
rebuild the entire tranny, but not how to simply change the lube.  Typical.
Anyway, I know that the drain (and fill?) plug is a 17mm hex job, and I can get
one of those at Sears, but I read in the archives that on some models
overfilling is necessary; ie through the speedo cable hole.  Do I do this, or
fill until oil drips out of the filler hole?  I am thinking of using synthetic
lube as well- any recomendations?  Oh yes, it is of course an autobox.  I think
that the diff is getting noisy and I don't know if the "mysterious evaporating
lubricant" has ever been replaced as recommended by the factory so long ago.
Any help is appreciated!

CDePenning
'83 5kT