1973 cj5 v8 rear axle

No assumption - I'm following Nick's lead on this - he's seen a lot of them. The picture is a little dark. However, it looks like a Trac-Lock to me too, though the picture is not the best. The Trac-Lock looks a lot like an open differential. Any LSD has to have a place for the clutch plates on either side of the spider gears. One side is surrounded by the ring gear, and hard to see, but the other side is out at the opposite end of the carrier, away from the ring gear. The LSD has to have a more cylindrical carrier, to accommodate the clutches on either side. The open carrier is more like a cone, tapering down on the side opposite the ring gear. However, the Trac-Lock has a lot of taper, compared to LSDs like the PowerLock, which is 100% cylindrical.

With an open differential, if the axle is in the car (and the driveshaft holds the pinion) with the wheels off the ground, you turn one wheel and the opposite wheel turns the opposite direction. Or, if you hold one wheel and turn the pinion, the opposite wheel turns. If it's a Trac-Lock, and it acts like an open differential, then the clutches are totally worn out. I know they wear out comparatively quickly, but I've never heard of one that worn out.

 

Brake cleaner is not what I'd want to get on any seals. It's pretty tough on rubber. Axle seals are enough of a pain that I'd not want to risk ruining them if they're not already leaking. If it were me I'd rinse it with lightest weight oil I could find, let it drain thoroughly, then change oil once after you have a chance to run it a while.