Just a follow up that I ended up replacing the whole front half of the case, the part is called the "front grip", and it only cost $12 from my lhs. Was a bit of a pain to change as you have to move all the rocker switches and remove all the buttons etc, but sure beats having no stops!

Futaba wouldn't own up to any kind of problem with the 4pl case so the only thing they'd do was give me the part #.