Buy the zinc from the parts store and follow directions. Put a thin layer of high temp rtv on both sides of the gasket will take up any pitting imperfections and hold in place for installation. No don't premix because you will probably have leftover gear oil in your container after you fill to the check hole while diff is level. No haven't touched the car lately been doing a lot of snowmobiling usually 100 miles or more each ride. Been a great winter for snow and cold temps in the mountains near me but unless things change it's coming to a close quickly.