Ladybug

The guy who put the sniffer to the evaporator -- which was exposed to our view with the glove compartment gone and the fan removed etc. out of the way -- says the tool is "stingy," meaning it doesn't beep about refrigerant unless there is an ample amount of such in the vecinity. And this is inside the cabin, under the dash and away from everything else a/c.
So it's gotta be the evaporator or expansion valve. (Insert prayer here.)
I know, huge difference as far as money and effort are concerned. He did say that he thinks the accumulation of leaves is similar to what he's seen before when leaves deteriorate and the resulting chemicals/acids eat into the evaporator. There was no dye at the expansion valve under uv light.
Whatever. He isn't trying to get my money, because he won't touch it -- once before, many, many cans of refrigerant ago, I used one with something that is supposed to stop leaks. Says it'll foul up and ruin his equipment. I doubt it, but I didn't argue.

Now, you mentioned something that catches my eye for the easiest way to do the job. Another friend who is a very good professional mechanic says he can't vouch for the Legend, but his experience with Honda/Acura cars tells him that the dash probably can be loosened, particularly on the passenger side, and pulled away enough (after loosening evaporator connections to the firewall) that the evaporator can be pulled down and out and replaced without taking the whole bejeebus dashboard out.

Whaddya think?