I installed a new dishwasher at least six months ago, all has worked just fine. But, recently water has been leaking out of the air gap on top and onto the counter top. I check everything and tightened up all connections. It is not leaking out of the gasket area but the top where the air is suppose to escape. Do I just replace the air gap every six months? sounds wrong. Or is because it is a plastic air gap? What advice can I get?