Tailgates for Steppies are harder to come by, good ones that is, there are a $hit load of Gates that are rusted underneath; also some have hinge problems.
When you replace the tailgate, two things, make sure the plastic hinge washers are in good shape and the holes the hinge part go in to are in good shape, replace any thing that looks bad.
Also, it would be smart (to me) to get new plastic parts for the hinges and put in a lot of grease and check the greased part every few months.
Should be a grease fitting on the hinges.