How about a spring in the rear to keep it pushed forward? I don't have one, so I'm tossing out thoughts only. Jim
Remove cover and apply 4 layers of electrician's tape to the little latch at the back of the tray. I have no idea exactly why this works, but it does. Cover will remain securely closed. To open cover, make sure it's all the way forward (to disengage latch), then lift up slightly on the BACK end of the cover and slide it open.
My armrest is perfect after I used epoxy glue to keep it closed forever. . You really can't put anything in it, so I just use it as an armrest.
A while ago one of the Vendors had a little knob that you'd screw into the back, the knob kind of looked like -+- with a small, self-tapping philips head screw in the middle. Install at the back of the sliding lid and you've got a "latch" of sorts. Turn 90 degrees to hold closed, turn flat to open. I suppose you can find something like that in the hardware aisle at Home Depot, Lowes, or Ace...
I must be on a different planet. The covers on both my former 09 Hardtop and current 2012 Roadster had detents (or is it dement, haha) that locked the cover in place, to my annoyance when I was hurriedly trying to open it. Our countryman has a hinged cover.
Dave.O: "MFin' thing wouldn't stay closed so I epoxied the SOB shut. That'll teach the f'er not to mess with my azz!" Word from a now-wiser armrest: "When Dave.O tells you to 'shut your yap', you might want to listen."