Had the same issue with some customers it was a mystery to myself and to Redcat it absolutely is a compression issue! The guys that had the trouble were running them in very dusty conditions which we chalked it down to the cause of the issue.

Try removing the ring under the head it may add more compression but I honestly think your engine is pooched, you can try doin a compression test as well.

Redcat will replace the motor for half the cost of buying brand new through the replacement plan.