I didn't notice the date of the original thread you blended your reply in so well.
It's due in for a service and MOT next week so I may let the Mechanic have a look then again it might be worth ordering the bit from S C & I and have the replacement done while they do the service. Do you have the part number or description that I can quote when ordering? Also would it be the same bit for a 620ie I note yours is a 900