Ignored Alarm then Prop Stopped

[bristolw66]

Good Morning Everyone!
I am a new owner and new to this forum.
I have a 2005 2100 SC, 350HP Alpha One and took it out to watch the fireworks this year.
While launching, I noticed an alarm and didn't know what it meant. On the way home I noticed difficulty engaging the drive, reverse seemed to work but forward seemed to weakly engaged. I took it easy on the way back, but 20 min later I dropped from 15 to 7 knots, then stopped. After 2am was finally towed in :-(

What I would consider the transmission, seems to be slipping then finally disengaged as if I was in neutral. In reading the forums over the last few day, Im wondering if the alarm was the Oil for the OD (Out drive?).

I'm about to take the boat to a mechanic, but any insight would help me.
Thanks, and I look forward to hearing from the community.

-Walter
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2005 Maxum 2100 SC
5.7L 350MAG 300hp V8 MPI Mercruiser