Beautiful pix of your lake!
About the dang bellows that is why many people here don’t want I/O boats and I wouldn’t buy another for myself either. Just too many places where they can leak water although I did mine 2 years ago and it’s still fine.
I looked at the pic of your pivot housing flange and it looked corroded at the top of the pic, wonder if it’s leaking there? The other thing is the grease tube. I recall reading over at iBoats (Volvo Penta I/o forum) some have eliminated that tube and replaced it with a grease fitting where the tube went into the gimble housing. That’s what I would do if I had a leak I could not solve. Are u using an OE bellows or aftermarket? I found the OE ones last at least 10 years.
https://flic.kr/p/TgKNqwthis pic....the next time you do the bellows use an OE one and use OMC gasket sealer or Permatex Aviation on both this flange and the one on the gimble housing. Make sure that the rib in the sealing surface of the gimble end of the bellows, really fits in that groove in the gimble housing flange.
thinking about the grease tube...try greasing the gimble bearing with the drive off and all the old grease and water cleaned off the bearing. If you see just clean grease coming out of the bearing, then I'd think its probably not leaking, but if you see grease that looks emulsified or watery it is a possibility.
last thing...looked back at your pix when you pulled the drive. I did not see grease on the nose of the bearing carrier that pushes into the pivot end of the bellows. In my OMC manual it says to put a good coating of OMC triple guard grease on the nose of the bearing carrier (the part that pushes into the bellows) and the lip of the bellows itself. When I remove mine each year that grease is still there. It will help seal it on that end.