I didn't retain my LSD when I swapped in the 4.77's - not sure I could have. So no additive needed in my diff. I forgot what I used when I did have the LSD though.
http://www.marvelmysteryoil.com/main.taf?p=1 I love this stuff! If stuck rings are the oiling issue with your 3.5, it might be worth it to get the spray bottle to shoot down the cylinders through the spark plug hole, let it sit awhile, crank the engine, spray some more, let it sit for a day, put the plugs back in, run it for a while, then change the oil and add a quart of MMO. Besides, it is a good idea to inspect the plugs if you are burning oil as they may be fouling.