A904 Leaking thru speedo

Hey guys I believe my speedo housing is leaking tranny oil. So I purchased the orink kit for it. When I remove the housing how much fluid could I expect to leak out there? Seems like a low place but not sure. Any trick to minimize the loss?

Also after assembly how do you fill the tranny? Through the small dip stick tube?
Yes you fill the trans back up through the fill tube. Warm, on level ground, in neutral. Block the wheels so it doesn't roll over you.