2. Yes, good suggestion, I'll have a look at that resiliant block; I'm pretty sure it is not missing...
Actually I meant worn through or at least very thin, not missing as in fallen out. Ie missing a thick amount of plastic; so, not much resilience left.
Wearing would be inevitable - dust and grit would settle and with each operation, erode some material. I think a new QR or at least a new piece of plastic would be worth investigating.
Are you lubing the sliding surfaces from time to time?