I’m fairly certain that the spring are strong enough. It’s fairly difficult to get them off and I doubt the pipe moves much at all. The inside of the pipe looks clean but I will double check as you suggest. The exhaust manifold groove are free from gunk but at least the last three grooves have some surface rust. I might run it though the sand blaster to make sure it’s clean. I’ll also try some of the high temp RTV you mentioned although I can’t even get that stuff to last back on the other end of the pipe between the pipe and the silencer.