Just filled differntial and manual four speed in my old 80 244 with synthetic gear lube.It's the difference between night and day.First gear was stiff before to get into now it is like a new transmission.It feels very mechanical now with positive gliding engagement.This car sat awhile.How long I will never know but the engine tranny and rear end magnetic drain plugs were disgustingly covered with gunk and micro metal.I am going to run it about 1000 miles and drain and refill again as its such a simple job and suprisingly it doesnt take too much oil to fill.Now the old girl is Amsoiled from front to rearand now tools down the road better than I had ever hoped...