"They had the most annoying property of the coupler spring rubbing on the outer axle so that at just the right speed....screeeeeeeeeeeeech."
I don't remember any of mine doing that. And, yes, I still have some in service. At least one is now 50 years old.
I'll bet if I look in my Rapido truck drawer of junk (and yes, I still have one!) I can easily identify them because the remedy was to pull out the spring and 'crush' it right above the axle so that it cleared, and then re-insert it. No more screech. They also had that unique and oversized bolster hole resulting in oddball plugs and clips for MT trucks that are now charmingly obsolete.
The other thing typical of the era was that Rapido couplers were ANYTHING but standard; Trix and Atlas were good, and believe it or not, MT made the best Rapido coupler when they used to sell cars with those on them. Con-Cor's were fat in all dimensions, stiff springs that wouldn't lift, and generally poorly made. The handful of us that actually every tried electromagnetic ramp remote uncoupling of them learned that. Was another great reason to go all MT and never look back. I'd had MT's in HO and welcomed them in N!