I tried silicone RTV first, before using the new o-ring but it didn't help. I will try the high vacuum grease or tape.I would use some high vacuum grease on the O ring to seal it up. Initially I would say use silicone RTV but there could be two issues with it. Some RTV will damage O2 sensors at least they use to. Second is that gas effects RTV. You can also just use adhesive tape to the joint to see it it changes things.
Thanks!