Differential cover question
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Don't use RTV and gaskets together, it will never seal. Most times gaskets are hard to find and typically not worth the extra money you pay for them. Most people, including the factory, use RTV to seal the cover. It doesn't really make that much difference which kind you use since they're all rated for oil and this is not a high temp application. I've used blue, black, and orange, they all work equally well for this. One word of advice when you're reassembling this, put a little bit of RTV on the threads of the cover bolts. This helps to keep the bolts from backing out, but they are still easy to remove when you put the wrench to them. I do this will all of mine as well as with transmissions and transfer cases.