I've heard some good things about GM's EOS(engine oil supplement) and want to know if anyone uses it? Actually what does it contain?...I've heard zinc and other heavy metals that the EPA doesn't like, so they are not in today's oil. If I use a quality oil like Mobil 1, do I even need this stuff?? Also, how much is a bottle? How many ounces is it? and does every GM dealer carry it?