+1 on Ultra Copper for both......never had a muffler loosen up on me and never had leaking of oil residue around the mufflers/engine.

Hesitated using Loctite only because I feared not being able to get the bolt out.......no proof that it would do so but just didn't feel comfortable using it.

But as with any other subject where folks have their choice of products/procedures do what you know works for you and be happy!

To much time wasted on the trivial and not enough on flying!