It's a common problem and one we have too. But our OC management pointed out: “Building defects are not within the standard scope of duties of body corporate managers and any work managers do is chargeable.” And also that: “Pursuing a builder through the legal processes can be very expensive – around $5,000.00 to start the process with a solicitor and expert reports and more than $30,000.00 if a barrister is eventually needed.”
Sadly, after 6 years, the builder is probably not going to do anything unless you start a legal process against him. Ours stopped returning calls etc. The OC has to decide if is worth the cost and effort in taking the legal path. So get some legal advice first. In our case the building defects are costing around $30,000.00 to repair, so taking legal action (which might fail) was not so attractive.
Ideally the builder should co-operate and fix all the defects, free of charge. But that's mostly just a dream.
Really it's the EC that should be directing the matter and making requests of the manager.