All the Unique that I have worked on have 2 solid mounts on the side pipe to frame on each side. I don't think they have a problem with cracks. I like to use one mount on the rear of the side pipe with a Mustang style rubber mount. I think it flexes better without breaking something. I have installed flanges on E-Ms and Shell Valleys. I have never seen a slip joint that did not leak.
Maybe if you run it rich till they seal up that would work.
We have tried a lot of different sealers on slip joint with little success.
got to go Coach just call and he is on his way to pick me up in his Coupe! road trip
Dwight