Originally Posted by
foama
If my memory is right, you need a normal 6mm allen key, the sort you find in just about every 1/4 inch ratchet box.
The gasket should be either a simple O-ring or an aluminium washer. I would put some Curil / Atmosit or any other stays-permanently-gooey type sealant on the thread of the bolt just to make sure.
Make 100% sure your choice of coolant is the correct stuff! If it just says "good for Mitsubishi" it is not good enough, because our cars have a different coolant than almost every other Mitsubishi model.
Thoroughly flush out the old stuff before refilling with the correct concentration.