Section 122 provides that the OC has the power to enter a lot to carry out works it is required or authorised to do under the Act.
You might not wish the works to proceed, but the OC has a duty to maintain and repair the common property. Look at it this way, if you had a moisture issue in your property wouldn’t you want it fixed?
Presuming there is no other way of fixing the problem, this leaves the matter of disruption in your space for 3 weeks and what you say is cosmetic damage to your courtyard. Disruption for 3 weeks is not major. As for the cosmetic damage, it would be reasonable for you to require the OC to make good the area, and section 122(6) provides that the OC is liable for any damage to a lot caused by it carrying out works under the section, unless they were obstructed or hindered. So I suggest that you reach an agreement with the OC regarding what they will do to fix your courtyard once the works have been done.