Re: New cartridge/o ring...still leaky!
Remove the cartridge and look down in the bottom of the faucet well. You should see a rubber washer in the hole where the water comes up, pull that out along with it's spring. It will be a small spring and a small rubber washer sort of shaped like a cup. Replace those two items. Thats what usually cause a faucet to drip, the "o" ring would cause water to seep out around the handle. At least that is the way our Delta works. It's item #19 in this drawing
Be sure you live your life, because you are a long time dead.-Scottish Proverb