2000 Yamaha F100 water in oil system

A few months ago I had an overheat due to a bad pump impeller. I replaced it, made sure there were not any extra pieces lodged up in the passageway. Then when I started the engine there was oil mixed in with the water coming out of the pee stream. I then replaced the head gasket, changed the oil/filter and that seemed to have fixed the problem, no more oil in the stream. Last week after boating home with open throttle in the cold weather, the next day went to start the boat and I had a very evident amount of oil mixed in with the water coming out the pee stream, more than it was months ago. I checked the oil level and yes it was about 1-1/2 quarts overfilled with water. Before I rip the motor apart again, I was wondering if anyone could give me some advice as to what might be wrong now, and/or any troubleshooting techniques.

I would do a leak-down test on all cylinders. Seems like the head gasket is still leaking, so there might be some internal damage that you didn't notice when you changed the gasket previously.

When you pull the head have it checked for cracks. I have had a few F90 engines with cracked heads and they filled the CC with water.