I'm still looking for that plastic piece if anyone can help.
Today I put the evaporator back in the box, and closed it up...DAMN that was a PITA job, trying to line everything up, with that rubber piece that goes around the copper pipes. It's still not 100%, but I think it's sealed, and I'll just wrap some extra dumb-dumb tape around it.
So, all the banging the thing about trying to get it to work, I began to worry I'd caused a problem. Then I remembered I'd bought this really cool Mighty Vac kit, and sooooo, I decided to put the thing under some vacuum and see if it holds. It's been a few hours, and I'll leave it over night, hopefully the temperature change won't cause it to lose vacuum. But, after 3 hours, it's been fine.