What do they look like? Are they the little rings made of excessively hard material with a steel ring in the middle that fits around a socket-head screw? (That's what my Dymag "cush drive" looked like) Overall dimensions approx 32mm OD, 16mm ID, and (IIRC) 10mm thick.
I ended up redesigning and replacing them with a combination of standard O-rings with a steel washer to act as a spacer to keep the O-rings from escaping through the gap between the socket-head and the inside of the sprocket holder. The purpose wasn't longevity (I was fully expecting to have to replace these after every race round - but O-rings are cheap) but rather in order to get non-zero cushioning. The standard "cush drive" was so hard that it provided no cushioning whatsoever, and I blame that for a gearbox failure in 2013.
It took some experimenting to get the combination of O-ring sizes right, but with that done, they actually stand up ... There is a plan to replace the ordinary black Buna-N o-rings with urethane of the same size and softness (70 shore A) but I haven't had to.
If your "cush drives" are those dimensions, I'll get you the O-ring sizes and washer size when I get home ... Remember, my objective wasn't durability of the cush-drive rings but rather durability of the transmission (which is a whole lot more expensive and containing unobtainium parts) but they have proven OK ...
