I was trying to replace a leaky shut off valve. I couldn't get compression ring off copper pipe w pliers so I put new valve on old ferrule & valve leaked more. Home Depot guy said his plumber father has tried placing a thin rope of teflon tape around both bevels of compression ring & put new valve on carefully. I carefully twisted tape into rope & double it over & twisted again. I put that on bevels as instructed & it seems to be working after a couple of hours. Firstly, has anyone else heard of this working? Secondly, is this a permanent solution or should I try to replace the old ferrule? Does the ferrule puller work? Any help would be appreciated?

I have tried that, and it didn't work. What I have made work in a case like that is a small O-ring between the ferule and the connector. Just don't tighten it so tight you squeeze the O-ring out. Do make sure you have several threads holding it together. It should last indefinitely with the O-ring.