Genuine Dyson DC04 soleplate rollers/axles pack of 5 rollers and axles

When would this part need replacing?
When some are missing
When they are worn or not spinning freely

Will fit DC04 clutch models including:

DC04 Absolute, DC04 Absolute Purple Lime, DC04 Brush control, DC04 De Stijl, DC04 Limited Edition, DC04 Zorbster.

Genuine Dyson DC04 soleplate rollers and axles X 5