Yes, there are a couple of orings on the speedo bullet. From what I remember, there is one on the outside of the speedo bullet and another on the inside, where the speedo gear goes through.
The bullet has to come out, to get to both of them. The bullet is usually a bitch to remove....it is usually corroded and stuck tightly in the tcase housing. Be sure to remove the bolt that holds the speedo cable in the bullet, before you try to remove the bullet. Sometimes you can get ahold of the outer lip of the bullet, twist it and it will come out. Other times you have to use a chisel on the outer lip to get the bullet to break loose and spin, so you can work it out. And other times it takes heat (a torch) to get it out....just be careful with a torch, aluminum melts at quite a bit lower temp than steel. When you put the bullet back in, put a lot of anti seize on it before you install it.