The biggest problem with the Gem engine was its oil distribution layout - the critical element was the white metal bearings in the reduction gearbox on the output shaft to the MRGB; they did not run without oil at all whereas the remaining bearings had a run-dry capability. So the reduction gearbox was the last location the oil went to before being scavenged which meant it was downstream of the filter. The filter had no bypass and blocked quite easily - the only indication you had was of the Oil pressure suddenly dropping from the green (stepped gauges) to the amber. If you didn't retard the SSL quickly the next thing that happened was the oil pressure dropping into the red followed by a large bang as the reduction gearbox seized. To my knowledge, this problem still exists despite several suggestions for modification and pilots are still having to shut engines down that, on inspection, are full of oil but have a blocked filter.
The only AFCS problem I encountered was the CAC (computer controlled acceleration) runaway; this happens in the collective channel when the accelerometers that are supposed to reduce collective pitch if they sense a rapid increase in 'g' go into a sort of open loop condition when the aircraft touches the ground and results in severe vertical oscillations (mine recorded +4.5 and - 1.5g on the g meter) - very exciting, especially when the CAC cutout is difficult to reach.