I got the new nut and installed it but I still have a exhaust leak at the manifold to cat pipe flange. I was told by the shop that there are no doughnuts it is a metal to metal seal and that I need a new cat pipe cost over $600. is there a cheaper way to seal this joint. need all the help I can get. Thanks

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TG's Ranger 2001 ext. cab, 3.0L, auto. 2wd 170,000 Bone stock