Massey 2706E wheel shaft seal leak?

[Garrett2006]

I noticed yesterday unloading a pallet from my trailer that the right side behind my front wheel looked wet. Figured it might have been some water dripping down from loader, but after I got trailer unloaded I checked the spot and it was oil. After looking in the shop manual. It seems as it has leaked gear oil from the top wheel shaft seal cover fill plug. Only right side the left is dry. Any ideas what would cause this? It痴 only supposed to be filled with fluid half way to fill hole from factory. Thanks