Toro Oil and additive
Unless you live near a torco dealer you can order the supplies you need from torcousa.com. You want the RGO 85/140 weight oil- NOT the synthetic stuff. It comes in a 1 liter bottle-you will need two. Also, you want the type "F" friction modifier, not the usual type "G" that GM rear ends typically use. Their stuff is very good- pricing is $12 per liter of RGO oil and $9.65 for a 4 ounce bottle plus a few bucks for shipping. I suggest that you also get a pump from your local parts store as you will not be able to add the oil with any type of funnel I've seen. The very bottom bolt is the drain plug and can be removed with a 13mm socket. The fill plug is at the upper right on the diff cover and requires a 30mm socket or a large adjustable wrench to remove. I would recomemend pumping in about 3/4 of the first bottle then adding 1.5 to 2 oz of friction modifier to that bottle and then finish pumping in all that remains. Switch bottles and finish filling up the diff. Replace the 30mm plug-DO NOT OVERTIGHTEN - just make it snug and you should be good to go.
06 GTO: GMPP Ported LS3 heads, CamMotion Custom Grind Cam, 102/102, OTRCAI, JBA longtubes & catless mids, 3600 Vigilante T/C, G-Force Engineering Drive Shaft, Driveshaft Shop Rear Axles.
95 Z - Intake, Exhaust, Cooling, 3.73 gears, PCM tuned.