Is there a reason why I shouldn't do away with the broken quick disconnect fitting on my lower trans cooler line and just slip the hose over the existing hard fitting past the flair and clamp it with fuel injection line hose clamp? My lower line already has a metal tube splice with hose clamps. (previous owner repair I assume)

Nope. Been done by lots of people.

Just be sure your hose is good ...and clamps are good.

Replacement lines aren't that expensive, btw. I just bought new lines (and tranny adapters) as the rest of my lines were pretty rusty (Great lakes kind of rust! LOL).

If you mean the one on the radiator, mine has a hose clamp on it too. Mine has the aux trans cooler so that line comes from the aux cooler. I do have a factory replacement hose with the qd on it. Next time I replace or remove the radiator, I'll put it on.

One thing to note, the bead on the pipe is pretty large so the hose may not slip easily over it.