Just read an article in my local "Landlord Times" paper about construction projects (and rehabs) built between 2000 and 2010 about the use of yellow brass fittings as connectors to plastic piping (PEX pipe).
According to Jerry Stein, a senior partner in a Seattle law firm, when water comes into contact with this fitting a process is started called "dezincification". The zinc component leaks out which weakens the fitting. The weakened fitting can cause leaks in walls, ceilings etc.
There are currently replacement of piping jobs being performed in buildings in the Seattle and Portland area. There was a lawsuit in Hawaii where the HOA won an award to repipe an entire high rise condominium because of the yellow brass fitting problem.
He suggests contacting an attorney if you have this in your property as remedies may be possible against the manufacturer.