I was lubricating the grease fittings on my M5140 this weekend and where the manual shows a fitting on the back of the front axle near the tire, there was only a bolt and a jam nut screwed into a hole. I don't know if there is supposed to be a fitting there or if I remove the bolt and add oil or just do nothing. This is a 4 wheel drive by the way. Is anyone familiar with this? Thanks!