Ducati MONSTER 821 Workshop Manual page 1140

Check the condition of centring bushes (25). If apparently distorted or loose in their seats, change them
using suitable tools.
When the centring bushes (25) are hard to remove from casing, use a left-hand tap to force bushes out.
Important
The bushes must always be replaced when they have been removed using the above procedure.
1140 Ducati Manuals Resource