Pretty much any 2-part epoxy will do the job.
You just got a lesson in mass production fly rods, and how little epoxy they use. It is so that can slide that threaded barrel on the reel seat and not have to wipe up any excess. If I build a rod or repair one like you have (it's happened to three rods, two of them factory Sages), I tape up the threaded barrel and the spacer where they meet. One thing about repairing a seat like that is that the butt cap is probably still affixed to the threaded barrel. Usually, the butt cap is the last thing to go on, and it leaves a place for air to escape as the reel seat is assembled. If you don't have the luxury of an unaffixed butt cap, as you slide the barrel back on the spacer, that epoxy is going to want to come out of the only gap available, which is where the barrel and spacer meet. And that is why I tape up both sides of that joint, as you likely will get some excess coming out there if you are applying enough epoxy to do the job right. Twist the barrel--a lot--as you push up on the spacer to spread the epoxy around inside the barrel.
The other thing about the butt cap being on is that you have trapped air in there, and it will want to force the barrel back off of that spacer. That epoxy acts like a lubricant until it sets, so you'll want to ensure that the barrel stays pressed up against the beveled edge of the spacer. Don't walk off and leave, because you will come back to find a barrel only partly mounted on the spacer, as it has slid back off.
Two schools of thought on the epoxy. Short set epoxies means the barrel and spacer don't have to be pressed together for as long before they set. Longer set epoxies give you more time to wipe up any excess glue that squeezes out or gets dripped on wood spacers, threads on the barrels, or the wife's new kitchen table. Pick your poison.