I bought a 9 bolt about 3 years ago with 89K on it and have had it sitting in my garage.
Decide to install it this week and was unable to get a full turn out of the pinion.
Opened it up and there must have been moisture in there that caused some rust to build on the exposed part of the pinion and ring gear.

I oiled it up and go it around all the way. (Rear did have probably original oil in it)

The question is obviously it needs cleaned out and probably at least one change of fresh fluid but should I add something into the first "good oil"?

Any other tips or shared experience is appreciated!

 

Cleaning out a rear end without taking it apart isn't easy. The space between the pinion bearings catches trash and it's very hard to get it out. I know that you don't want to take this apart, so you are going to have to flush it with mineral spirits or something to try to get as much out as you can. Then be sure that whatever you use to flush it has dried or evaporated completely before putting oil in it again. There is also going to be rust in the axle tubes, but removing the axles may damage the seals. If you damage the seals then you will have to replace the axle bearings. There is also a good chance that some of the bearings have rust on them too. I wouldn't expect a lot out of this rear end as it is. You may have to rebuild it after a little use.