Discovery of Modifications to Common Property after buying Unit

Hi Jimmy  What is the correct area or section that covers things like the OC is responsible for any changes that might have been done by previous owners before they sold the unit to current owners. 

For eg:-  We bought the unit in good faith , had it inspected and cleared of any major faults before buying it in 2010. Recently a TV antenna installer discovered that ceiling joist have been cut to install down lights . The down lights were there when we bought the Unit.

Strata Manager has asked that all ceiling joist to be repaired and down lights installed must be made to conform to AS/3000-2007 ,Fig:-4.7 All work to be certified, by licensed person. 

I did contact the original building inspector re the ceiling joist and he is of the opinion that it is common practice and the joists are strong enough to hold the ceiling up. The joist don`t need to be repaired.  

Regards , Thanks.