Your ok to try to just replace the o/rings but the man. is prob. worn/out by now and may be smart money to replace it, before you have to redo your work?
That's what I did. It wasn't that much more to do that and that way I knew I wouldn't be back under there for that particular problem again......I found another leak though while I was checking for leaks after installing the manifold. Something else I'll need to replace as well.