No. Sealant is optional but some use Teflon tape, which I don’t like. It breaks down quickly. Sealant preserves the threads and makes it easier to remove the plugs later. They have a tendency to corroded in place. I’d use a torque wrench though.Thanks. My manual rear diff has two 13MM square female plugs. I already have the 2 flat OEM gaskets. Do I really need to use thread sealant? CVT rear diffs have different drain and fill plugs.