5N-AYX
A quick check online confirms that Dave B's photo is indeed #30599 which was the famous 5N-AYX, as posted on Page 36 of this thread.
No-one really understood the collective to cyclic mixing until the Check 2 when the famous hellhole crack was fixed. We had stopped using 5N-AYX for No.1 Hydraulic failures after a rather abrupt arrival to the old helipads on a base check.