One of the fine epoxies formulated for rod building applications are your best bet. I prefer U-40 permagloss, but I think I've seen small packages of flexcoat, which is also popular, on shelves at Dicks and Bass Pro. Not a bad idea to have some on hand just in case. Other epoxies may produce unexpected results.
If they are coming undone, it may be best to remove and replace the old thread and epoxy. Tons of great you-tube video's on how to do it, you just need to the rod building thread and epoxy, or...... If you're in the area on the north shore, let me know, and I can do it for you or show you how and you can do it yourself.
http://www.mudhole.com/Rod-Building/Epoxy-Finish