I don't think that the direction of the spring washer will matter. The FSM doesn't mention anything other than putting everything back together and installing the cotter pin. The axle nut is tightened to 180 ft. lb., is doing ALL the work, and will not loosen unless someone screwed up really bad. That sheet metal cap is just there as an emergency stop if the axle nut should somehow come loose.
I think you might be right that the spring washer lost some of its strength, allowing the lock cap to rattle. You might have been able to remove the old spring washer and bend it to restore enough pressure. You could have just bent the cotter key a bit to hold down the lock cap. Or, you could have taken a punch and bent that lock cap a bit so that it could not rattle. It provides no structural strength. A bit of RTV under the cap would stop the rattle too.
I prevent all that rust by painting those parts with fluid film, anti seize, etc..
2014 Sport, 2wd, 2.4L, 6 speed tranny, Winter Chill
Last edited by Treegrower; 05-18-2017 at 09:11 PM.