Easy fix fella. As said above make sure 2 faces are clean where the dust sheild goes into housing run screw driver around there also then put light Nickle coat in that grove area. Light amount. Then if you have a propain torch or gas set heat up that edge around exhaust housing. Not alot . All warm to touch is enough. Heat exspands it some put,core on top put bango clamp on let cool. Thats how i do them worked every time was shown how to do that by turbo speacilist years ago. The heat trick on exhaust housing lip is also good for dismantling aswell instead of big hammer bashing it lol