Hi Nick,
First I will tell you I have never worked on a BF25 so you may get better answers from others here.
Second, I hope that the cranckcase isn't overfilled due to gasoline dilution. Do you/ did you smell gas in the oil? If so, you need to find out what is causing that before running it any more. A leaking fuel pump would be my #1 suspect for causing major fuel dilution of the oil.
If you believe that there's no fuel dilution and suspect poor venting of the sump, I can tell you that the crankcase is vented through the valve cover to the intake muffler cover via a molded hose. See item 10 in the link below. That is illustration page E1430 of the parts manual.
https://www.boats.net/catalog/honda/outboard/25hp/bf25dk0-lrta-2007-and-later/muffler-cover
The note for the vent hose shows you to reference parts page E2. Here's the link to that page:
https://www.boats.net/catalog/honda/outboard/25hp/bf25dk0-lrta-2007-and-later/cylinder-head
You can see the nipple on the valve cover where the vent hose connects. It is highlighted by a reference back to page E1430 in bold type.
You will also see that there is a different, larger diameter hose connected at the valve cover. Item 15. There they direct you to reference page F-8. Here's the link to that page:
https://www.boats.net/catalog/honda...0-lrta-2007-and-later/engine-cover-lower-case
You can see from the bold type E2 reference that the hose attaches to the lower case on the port side rear area of the case.
That is where my knowledge of this ends. I don't know the actual function of that hose. I'm not going to guess either because that would only confuse the issue.
I can only tell you that you may want to pull the valve cover and investigate why the vent might not be working.
Good luck.
