I do this about five times a year and Wal-Mart sells a kit with glue and three different size tips for about four bucks. Just make sure you get it in line and don't lean it up against the wall before it is dry. a "friend " told me that it will knock it out of line if you do that!haha
I'm always afraid that I won't put on enough glue - so I end up having extra pushing out around the end of the guide after I've slipped it on..... I just wait until everything is cooled and then trim the excess off with a razor blade or sharp knife - Carefully! So that I don't nick the rod.