How can you have 30-year old receptacles and not have the plugs slide out of them????
Here in the U.S. you're lucky sometimes if you can get one of those things to last 5 or 10 years before the face cracks, or the contacts inside loose their spring-action and plugs fall out all by themselves.
Granted that's more the case with the cheap "residential-grade" 50-cent piece-of-craps you see from the big DIY sheds than with the more expensive, but tougher, commercial-quality ones.
A long time ago, I bought one (made by General Electric) and as I started to tighten the screw, I felt it grip and then slip. Guess what, the thread had stripped off near the top of the screw's head!!!!
And what's even more astounding is when you see these things (they're easily recognizable - especially the Leviton ones) being used in professional installations and you see a socket broken clean in half and dangling inside the box!!
I'd be very uncomfortable using second-hand devices or anything that I didn't personally buy and check out...but that's just me. I've gotten overly cautious since I found this forum.