Three problems are common with those Boston hitches in my experience with them. The first one being the small spring on top of the latch rusts out and wont hold the latch ALL the way up, often you will see them "fixed" with a bolt through the sides of the operating slots. The test is easy, grab the latch and pull up, if it moves the spring isnt strong enough and needs replaced. If it has a bolt in it instead of the spring get rid of it.  Second thing is the contact area that actualy does the latching is worn. Hard to discribe but easily seen. fix is Mr welder and grinder. Take a look inside and how it moves and works and build up the worn areas. Third thing is those large springs on the side. Sometimes they sag with age but more often they are bound to the bolt with dirt/rust and cannot do thier job.