The JR G770 3D gyro, with a good 4 or 5, maybe 6 hard crashes on it.
I noticed an odd tail kick while in a hover that would decrease in amplitude when I turned the gain down. If I changed head speed it would go away all together..
Turned out one of my unscheduled landings broke the glue joint holding the gyro circuit boar in place. The result was the board was bounching around inside the housing and would make the tail kick (not much, maybe 3 or 4 degrees, but it was rather violent.)
As a field repair I put the furry part of some velcro on the gyro lid, and screwed it back together. Sadly, the fix may become permanent :)