Loctite 648 is very good, and will indeed hold a gear on an arbor. But it needs a certain amount of surface area. I can pretty much assure it won't hold a sweep seconds hand on a pipe. Honestly aside from making a new pipe, solder is the best route. You'll want a good flux, it will get it to flow and hold to the steel hand. Tix is a brand of soft solder and flux that will 100% sure work with steel and brass alloys. I have good luck with regular electrical solder and flux too. I heat the assembled hand and tube on a little brass plate over an alcohol lamp. Put flux and a tiny piece of solder at the joint. Since you're already repainting the heat is a non issue.
The best I've found is either CousinsUK.com (Go to watchparts>Branded>Omega>Case parts and search by Ref Number "145.036".
Now the second best has been http://cgi.julesborel.com/
Cousins tells me its a: Glass, Mineral, Omega TN5250
It appears to be a flat mineral crystal.
Some of the photos make it look like a domed crystal.
Either way genuine is around $60USD: https://tmwatchco.com/product/new-genuine-omega-flightmaster-crystal-145-036/
I wouldn't stuff around with an aftermarket on such a watch unless you are qualified to measure and size one up yourself.