1. How can i figure out if i have a 9 or 10 bolt? RPO codes maybe? 2. My diff is leaking, what type of sealant should i use? (silicone?) 3. what gear oil is the best?

9 bolt = 9 bolts in the cover. 10 bolt = 10 bolts in the cover. Any 80W90 or 75W90 gear oil will be fine, but I use Amsoil. Where is the leak?

Thanks thats what i figured, but i havent been under the car to check. From what i can see it looks like it is comming from the lowest part of the "meatball"

As far as sealant, what do you use?

I use a gasket. Many use RTV.

JamesC

I haven't used any sort of diff cover gasket on any diff I've worked on for years. RTV works fine. I usually use Permatex Red (it's orange).

80W90 or any synthetic gear oil will work fine. If you have a posi, a posi additive should be used. GM makes the best posi additive and it stinks worse than a pig farm.

My race car uses 75W90 Lucas oil in the diff that one of my sponsors provides.

Check the pinion seal. Many times the pinion seal will leak and the oil runs back to the rear of the housing and it just looks like the gasket is leaking.

Good point. I saw some leakage and just figured it was the diff leaking. thanks.