There is a trick to installing diff gaskets and oil pan gaskets on the wedges. Coat both sides of the gasket lightly with your choice of sealant, and let it sit for a few minutes so that it starts to dry. I like black RTV because it doesn't look stupid when it squeezes out like the red stuff does. Install the gasket, cover and bolts, but only tighten them a little bit. Go back the next day after the sealant has had a chance to set and torque the bolts down. If you try to torque it down with the sealant wet, the gasket will stretch and squeeze out the sides.