Rick,
A couple of things you can do---

One is simple, the other's are not so simple.

In the event of an emergency, such as you described, simply pull of the
hose to the fill tank, and loosen up the pressure cap on the expansion
tank.
Not too much----- just about a 1/8th of a turn will relieve enough
pressure to slow or stop the leak enough to get you home.

I did this 2 months ago, when one of the engine hoses split---got me
home, and back to work the next morning with zero leakation.

And as far as replacing the "H" coupling, I would go to "Ace is the
place" and fabricate the piece from pvc, or copper tubing.
I think the copper tubing unit, soldered together, would be a bullet
proof solution.

Or you could purchase some 3-M body panel adhesive, and rough out the
crack, and apply some of this stuff-----it is the only thing I know of
that will permanently bond polyurethane, or polystyrene.

But the catch here is that the stuff is expensive,and comes in a larger
quanitity than you will need---just hope you have something else you
might want to permanently glue together----

Later,

            ______________
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     ~~~ ~||-(())----(())-|

Terry--
74 Campmobile- (Clementine)
85 GL- (Delilah)
86 BMW 325 ES- (Eva)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~     "In life, it is much better to want
something you cannot have---

Than to have something you can't get rid of"

(T.K.)