Moen two handle bathroom faucet - new cartridges but still drip
There is probably some hard water deposits inside the valve where the cartridge O rings and seal make contact. The slightest deposit will break the seal and you'll have a drip. Get some fine emery paper and gently clean out the valve making sure it's totally smooth inside. Then get some plumber's grease, coat the cartridge and reinstall. Hopefully you didn't damage the O rings inserting the cartridge the first time.