Rebuilding gear box volvo penta 4.3L GXI

[The Mermaid]

I have taken apart the gear box in my Glastron volvo penta. I will replace all bearings, and the bearing housing, as the bearings fell out when I took it apart.
QUESTION: Do I replace the gear (#18) if it looks intact? Given the bearing housing was altered, how do I know what to replace in front of it/in back of it? All of that energy had to go somewhere. Thanks.