Okay so i have this 2002 WS6 3.42 posi rear, and the right side shaft broke, i got a new shaft sent to me, now i need some gear oil, and my pops said i needed some type of additive for that since its a limited slip, and then a certain gasket or some type of silicone to seal it...can anyone help me figure out what i need???

GM Limited Slip Additive is what you need, one bottle. Your local chevy or pontiac dealer will have it for about 5 bucks. They will have the differential cover gasket you need also. You can install the gasket dry, or use a little rtv black, orange, whatever.