I Went Through Eactly ....................
................ the same thing three days ago, and I don't mean almost.
I had to remove the existing #10-3 wire and replace with another piece of #10-3. Fortunately, the old wire was able to come out freely.
You're right in using only the very best, cast iron, bomb proof, connectors money can buy on this one. Much easier than trying to remove the glued in shell.
Don't know which old receptacle you're replacing, but I was replacing a Marinco receptacle. I found that the side and bottom landings for sealing were getting pretty narrow (about 1/8") with the new SmartPlug and decided to discard the rubber gasket which came with the receptacle. I used butyl rubber instead and applied a little heat using a hair dryer to squeeze out the butyl from the wider parts. Having extreme OCD, I then coated the prongs with Super Lube and finally wiped down the cord with Meguiars Vinyl Rubber Cleaner & Protectant.
If that doesn't last for at least 100 yrs, I'll be somewhat ticked.