Two of my three trucks turned out to have factory lockers installed.
The Desert Scout (1979 Scout II 50k original miles) did not have a locker. Line setting ticket shows axle code 14018, this refers to open carrier Dana 44 which was standard on a Scout II. So the desert Scout is going to get an upgrade to our Yukon locker kit. This upgrade will ensure traction from both rear wheels when climbing a dirt hill.
The Farmer Scout (1979 Scout II Terra 150k original miles) does have a factory Dana Trac-lok installed which is great. Line setting ticket for this truck shows 14028 which refers to the factory installed Trac-loc limited slip rear. With the Trac-lok installed there will be no reason to upgrade to the aftermarket locker for this Scout II. I will change the fluid and gasket on this axle.
The Mountain Pickup (1968 1100C Travelette 4×4) does have a factory installed Powr-lok differential. Line setting ticket for this truck shows the 14054 axle code referring to the Powr-lok equipped rear axle (14053 refers to the open carrier). The Powr-lok and Trak-lok are friction clutch systems, so when I change the oil I will add the correct additive.