The Dexter axles are hard to see the oil level in. They don't have a clear window like the big rigs do, at least the ones I have been around. The best bet is to pull the plug and fill it to just below centerline of the axle. Use a good 90 wt oil and it will be fine. A little seep by the plug is not bad. What is bad is if you see oil on the back of the wheel. That means a seal is bad. Better fix that pronto, or it will loose oil on the road and seize the bearing. When not caught in time, this leads to the tire and wheel, with hub attached, leaving you and going for a ride of its own.