It will be a flexible hose or tube attached at the top of the housing and have a check valve in the end of it. You should see it go upwards and be attached somewhere so that it cannot fall away. It is there to vent pressure in the diff. If is kinked or clogged the pressure builds up and the seals will leak and even new seals will continue to leak. I would assume Meineke checked that but I would ask them. Once the seals starts to leak it will continue but the rate will be drastically reduced if you happen to have a vent problem and fix it and don't change the seal.
