Sounds like you may have aftermarket exhausts fitted, ie some form of performance system, as you mention that they are just held on by springs, this is the normal procedure for aftermarket systems such as jha, tyga, jollymoto, and a host of others, they simply push over the collars, supplied with the pipes, and are secured by the springs. You will need some sealant to get them to seal reasonably. If your'e not worried about originality, leave them on,a lot of people would give their high teeth for a set of aftermarket pipes for an mc16. Good luck with it.