pull the flywheell cover and check the flywheel for up\down and SIDE movement ,
U could even run the motor and visual watch the flywheel for movement
if it moves up/down is usually a sign of not trued withen spec crank
The vibration and stress on bearings is not the only issue with a non trued crank, as is rotates it will be slightly changing in width [more than the clearance in the c3main bearings ] which will force the main bearing spin\move sideways on the shaft, [common on the kx }
I think we should all be anal about about truning our cranks
maybe not your problem but worth a check as 50% of kx5 motor have spun bearing on crank, maybe i am really unlucky with kx5 motor