4HP Leaking Oil in Lower Unit

[nicksorg]

I have a 2006 4 HP (F4MSH) that I ran today in a tub of fresh water. While adjusting the lower shift shaft? to get it to go into reverse, I noticed there was some oil drops coming out of the seal right behind the shaft. I'm mechanically inclined, but new to outboards. In the pic, the red marks show the gap where it was leaking. Can someone tell me what is involved with fixing this and what those seals are called?
Thanks
Nick

[boats.net]

Would need to remove lower unit to see if it's gearcase oil or engine oil thats leaking.