Possible leak repair
This is probably a crazy idea but when situations arise like this sometimes the craziest things work. If you know where the leak is, can you possibly rig up something like this where you can apply some 5200 sealant to the inside of the hose using a small vinyl hose attached to the tip of the 5200. Just liberally apply it around the area of the leak then possibly spread it around with a 1/4" or 1/2" flexible copper tube . Since there is minimal water pressure and the leak hole is probably fairly small, any 5200 that gets there may seal it up.