Genuine Dyson DC25 washable HEPA post filter

When would this part need replacing?
After the motor has failed
When the pre filter has not been washed often enough causing this filter to block too.
When the filter cover pops out from the ball
When the machine makes a noise like a balloon going down when you switch it off (air leak).

Fits The following DC25 models:
DC25 Overdrive, DC25i, DC25 Multi floor, DC25 All floors, DC25 Multi Floor exclusive, DC25 Animal, DC25 Blitz it, DC25 DRAWING Limited edition

Genuine Dyson DC25 HEPA post filter 916188-06