any special filler neck cap? and coolant flush question
 

I was looking at the radiator filler neck, and the cap on it has a little rubber "seal" on/in it, but that seal is now torn. I can't remember offhand, do all radiator caps come with this? And if so, should I just go to autozone and pick myself up a .9 bar radiator cap?

forgot the coolant flush question.. if I warm it up, take it to a shop, and they do their whole coolant flush machine thing, is that going to be bad (180+ degree water, quickly switched with unknown degree water).