was it a new sleeve? i had to replace one on mine when i dropped my exhaust, the other clamp i hammered the bolt fittings wider so it would clamp more. also was it the right one? theres 2 different ones, one for in front of the middle pipe and one behind and there slightly different, same size tubing but the clamps have slightly different bore.
or just get some exhaust flexi and some mikalor clamps if you dont wanna go down the welding route