As hydroponics and aquariums meld into one hobby for myself, you made my day!
Rebuild it would be the answer.
If you can't find the replacement for the plugged end you could put a cap on it and after predrilling a hole, tap it to accomadate whatever size nipple for the smaller hose you want. The thicker the cap, the more threads you'll have to hold the new nipple in. As you have chemically reative conditions, you may see if there's plastic threaded ones available. If Homers, Nards (*******), Lowes or a better aquarium supplier can't help you, there's janitorial supply places that service steamcleaners, and pool suppliers (think sodium hypochlorite or calcium chlorite and ect.). Some outfits sell supplies for both and may be a source for ideas where to get specific items. Or considering the price of the standard brass and time expedediency buy a couple as maintanance protocol.
As you probably figured out allready, you have to have a certain amount of surface area available before glue would be viable. And as with any plumbing or electrical design, male to female is the best coupling